boards : arm : Add support for Microchip MEC15xx EVB ASSY 6853

This was tested with the hello world application. UART 0 was used
as console for displaying "Hello World! mec15xxevb_assy6853" to
the serial terminal.

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

soc : arm : microchip_mec Use rename fault clear function

The Cortex-M core function to clear faults was rename by
upstream. Update to use new name.

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