configs: deprecate dmc-620 ras support

sgi575 and rdn1edge support dmc-620 error handling. Deprecate the
dmc-620 ras support as that ip is old and providing a reference code for
discontinued ip is not correct.
Also for now disable the firmware first support on sgi575 and rdn1edge
as just enabling the framework without any error handling driver will
add no value apart from increased code redundancy.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I2ae547696f0c66901ad68f28cde36dd308f21592