drivers: i2c_sam0: Optimize i2c

Optimizations:
When using system power management, the bus transactions
can be interrupted by low power modes which causes excessive
power consumption and can cause the transactions to terminate
before completed. Further, other interrupts can cause bus transaction
anomalies.

When using the RESTART flag, the MB and SB bits must be cleared.

This commit prevents interruption of the bus during low power modes and
correctly clears the MB or SB flags when a bus transaction is restarted.
Also fixes an initialization problem with the INACTOUT timer and ensures
the LOWTOUT is properly configured when using i2c_configure().

The GCLK_SERCOM_SLOW clock is used to time the i2c
time-outs and must be configured to use a 32KHz oscillator.
See 28.6.3.1

This commit configures GCLK4 to 32768 Hz

Fixes zephyrproject-rtos#21711, zephyrproject-rtos#21549, zephyrproject-rtos#21233, zephyrproject-rtos#21232, zephyrproject-rtos#21114, zephyrproject-rtos#21092

A problem can arise when back to back transactions occur before
the STOP transaction is complete.

This commit also introduces a busy wait for the STOP to complete
with an timeout in the event there is a bus failure.

Signed-off-by: Steven Slupsky <[email protected]>

Author: sslupsky