Don't build level zero provider in non-l0 builds

We don't need it, and this saves a repo fetch and some compile time.

Author: RossBrunton

source/common/CMakeLists.txt

@@ -7,6 +7,8 @@ if (UR_BUILD_ADAPTER_L0 OR UR_BUILD_ADAPTER_L0_V2)
     include(FetchLevelZero)
     set(UMF_BUILD_LEVEL_ZERO_PROVIDER ON CACHE INTERNAL "Build Level Zero Provider")
     set(UMF_LEVEL_ZERO_INCLUDE_DIR "${LEVEL_ZERO_INCLUDE_DIR}" CACHE INTERNAL "Level Zero headers")
+else()
+    set(UMF_BUILD_LEVEL_ZERO_PROVIDER OFF CACHE INTERNAL "Build Level Zero Provider")
 endif()
 
 add_ur_library(ur_common STATIC