ec_chip_mchp: Lower UART interrupt priority.
ec_chip_mchp: Lower UART interrupt priority.

Reduce UART interrupt priority to not interfere with
critical interrupts. WDT highest, GPIO & other HW,
UART, Port80(lowest).

BRANCH=none
BUG=
TEST=Build boards based on chip mchp.
CQ-DEPEND=CL:1053576

Change-Id: I293132fce46cc460d1cf51abacf4b6a494c8c4a3
Signed-off-by: scott worley <186210b307f58d6c0a191337b635ed93ad075837@microchip.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/1053873
Commit-Ready: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Tested-by: Scott Worley <186210b307f58d6c0a191337b635ed93ad075837@microchip.corp-partner.google.com>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec