[SYCL][L0] Update SYCL_PI_LEVEL_ZERO_USM_ALLOCATOR description (#12088)

The description is no longer correct.  Default values have changed.

Ref:
https://github.com/oneapi-src/unified-runtime/blob/main/source/common/umf_pools/disjoint_pool_config_parser.cpp#L27

Author: igchor

sycl/doc/EnvironmentVariables.md

@@ -247,7 +247,7 @@ variables in production code.</span>
 | Environment variable | Values | Description |
 | -------------------- | ------ | ----------- |
 | `SYCL_PI_LEVEL_ZERO_SINGLE_THREAD_MODE` | Integer | A single-threaded app has an opportunity to enable this mode to avoid overhead from mutex locking in the Level Zero plugin. A value greater than 0 enables single thread mode. A value of 0 disables single thread mode. The default is 0. |
-| `SYCL_PI_LEVEL_ZERO_USM_ALLOCATOR` | [EnableBuffers][;[MaxPoolSize][;[host\|device\|shared:][MaxPoolableSize][,[Capacity][,SlabMinSize]]]...] | EnableBuffers enables pooling for SYCL buffers, default 0, set to 1 to enable. MaxPoolSize is the maximum size of the pool, default 0. MemType is host, device or shared. Other parameters are values specified as positive integers with optional K, M or G suffix. MaxPoolableSize is the maximum allocation size that may be pooled, default 0 for host and shared, 32KB for device. Capacity is the number of allocations in each size range freed by the program but retained in the pool for reallocation, default 0. Size ranges follow this pattern: 64, 96, 128, 192, and so on, i.e., powers of 2, with one range in between. SlabMinSize is the minimum allocation size, 64KB for host and device, 2MB for shared. Example: SYCL_PI_LEVEL_ZERO_USM_ALLOCATOR=1;32M;host:1M,4,64K;device:1M,4,64K;shared:0,0,2M|
+| `SYCL_PI_LEVEL_ZERO_USM_ALLOCATOR` | [EnableBuffers][;[MaxPoolSize][;[host\|device\|shared:][MaxPoolableSize][,[Capacity][,SlabMinSize]]]...] | EnableBuffers enables pooling for SYCL buffers, default 1, set to 0 to disable. MaxPoolSize is the maximum size of the pool, by default there is no size limit. MemType is host, device, shared or read_only_shared. Other parameters are values specified as positive integers with optional K, M or G suffix. MaxPoolableSize is the maximum allocation size that may be pooled, default 0 for shared, 2MB for host, 4MB for device and read_only_shared. Capacity is the number of allocations in each size range freed by the program but retained in the pool for reallocation, default 4. Size ranges follow this pattern: 64, 96, 128, 192, and so on, i.e., powers of 2, with one range in between. SlabMinSize is the minimum allocation size, 64KB for host and device, 2MB for shared and read_only_shared. Example: SYCL_PI_LEVEL_ZERO_USM_ALLOCATOR=1;32M;host:1M,4,64K;device:1M,4,64K;shared:0,0,2M|
 | `SYCL_PI_LEVEL_ZERO_BATCH_SIZE` | Integer | Sets a preferred number of compute commands to batch into a command list before executing the command list. A value of 0 causes the batch size to be adjusted dynamically. A value greater than 0 specifies fixed size batching, with the batch size set to the specified value. The default is 0. |
 | `SYCL_PI_LEVEL_ZERO_COPY_BATCH_SIZE` | Integer | Sets a preferred number of copy commands to batch into a command list before executing the command list. A value of 0 causes the batch size to be adjusted dynamically. A value greater than 0 specifies fixed size batching, with the batch size set to the specified value. The default is 0. |
 | `SYCL_PI_LEVEL_ZERO_FILTER_EVENT_WAIT_LIST` | Integer | When set to 0, disables filtering of signaled events from wait lists when using the Level Zero backend. The default is 0. |