boards: microchip: mec_assy6941: Add MEC5 evaluation board 6941

We added the mec_assy6941 an evaluation board for MEC5 HAL based
MEC174x and MEC175x parts. We support these Microchip chips:
mec1743_qlj, mec1743_qsz, mec1753_qlj, and mec1753_qsz. LJ refers
to 176-pin and SZ to 144-pin WFGA packages. Q refers to total SRAM
of 480KB. Building the board with one of the SoC's requires passing
mec_assy9641/<soc_name>. For example: mec_assy6941/mec1753_qlj is
passed to west via the "-b" command line option.
The SoC's are configured to use Microchip's 32-bit 32KHz RTOS timer
as the kernel tick. Refer to the board DTS rtimer node. If the user
wishes to use ARM SYSTICK as the kernel timer then disable the rtimer
node in the application overlay.

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