drivers: espi: Microchip MEC172x child host device interrupt priorities

Set default interrupt priority to 3 for all Microchip MEC172x eSPI
host child devices except the UART's which are set to 1.
The espi peripherals don't require the maximum priority hence they
are being made uniform and a lower priority 3.

Signed-off-by: Jay Vasanth <jay.vasanth@microchip.com>