sp_metadata: add a new entries to DTS for RAS specific carveout

CPER memory region carveout is added to the STMM DTS file.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I30ca6b0e60c2741474f70bece7c40d213a42f2ad