ci(coverity): add coverage for FEAT_SME2

This patch adds a build config for SME2 to tf-cov-make,
to ensure that the relevant code and files are scanned.

Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
Change-Id: I98da19e1fda1e89a5845fe0497371ec8d6572573
1 file changed