drivers: timer: mec5: Driver using Microchip RTOS timer as kernel tick

Timer driver using Microchip 32KHz based RTOS timer as the kernel
timer tick. The driver uses one of the 32-bit basic timers to
support the kernel's k_busy_wait API which is passed a wait
count in 1 us units. The 32-bit basic timer is selected by using
device tree chosen rtimer-busy-wait-timer set to the handle
of the desired 32-bit basic timer. If this driver is disabled,
the build system will select the ARM Cortex-M4 SysTick as the
kernel timer tick driver. The user should specify RTOS timer
as kernel tick by adding the compatible properity and setting
the status property to "okay" at the board or application level
device tree. The driver implements two internal API's for use
by the SoC PM. These two API's allow the SoC PM layer to disable
the timer used for k_busy_wait so the PLL can be disabled in
deep sleep. We used a custom API so we can disable this timer
in the deep sleep path when we know k_busy_wait will not be
called by other drivers or applications.

Signed-off-by: Scott Worley <scott.worley@microchip.com>