dts : arm : Add Microchip MEC1501 SoC device tree

Initial support for Microchip MEC1501 series is added to the tree.
Additional support for UART is also included. This SoC supports
two operational modes for interrupts (Direct and Aggregated). For
this commit, the direct capable interrupts are configured in
direct mode.

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