Platform/ARM: Add DMC-620 ECC error handling driver

DMC-620 memory controller improves system reliability by generating
interrupts on detecting ECC errors on the data. Add a initial DMC-620 MM
driver that implements a MMI handler for handling single-bit ECC error
events originating from the DRAM.

The driver implements the HEST error source descriptor protocol in order
to publish the GHES error source descriptor for single-bit DRAM errors.
The GHES error source descriptor that is published is of type 'memory
error'. A GHES error source descriptor is published for each instances
if the DMC-620 controller in the system.

The driver registers a MMI handler for handling 1-bit DRAM ECC error
events. The MMI handler, when invoked, reads the DMC-620 error record
registers and populates the EFI_PLATFORM_MEMORY_ERROR_DATA type error
section information structure with the corresponding information read
from the error record registers.

Co-authored-by: Thomas Abraham <thomas.abraham@arm.com>
Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I2530b174c5398c2db86220200fa29ecfdcc5cca1