build(rzg): separate BL2 and BL31 SREC generation

This small change creates individual Make non-phony targets for the Bl2
and BL31 SREC binaries to avoid rebuilding them unnecessarily.

Change-Id: Ia8e5db0e4a968d4b379fdb66123b6a8f20933bf5
Signed-off-by: Chris Kay <chris.kay@arm.com>
1 file changed