soc: microchip: mec: Unify kernel timer tick rate configuration

Microchip MEC was configuring the kernel timer tick rate at the
board level instead of the SoC level. We unify all this by moving
the Kconfig logic out of the board level into each mec chip.
We also derive SYS_CLOCK_HW_TICKS_PER_SEC from the device tree
node enabled for the kernel timer: Microchip's 32 KHz RTOT timer
or Cortex-M4 SYSTICK. The soc kconfig rules are loading all mec
subdirectories for every build causing warnings when building
new socs with this change. We made the changes for all the mec chips.

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