refactor(build): update build string to show rc-tag

The build string has been updated to reflect the rc-tagged version.
The change has been made to be in line with the TF-A.
The build string has been changed now as follows:
	NOTICE:  2.6(fvp,debug):v2.7-rc0
and, previously it was:
	NOTICE:  v2.6(fvp,debug):207353c

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: I79f31750f3bc6bacc118e9c567b5c9f9dd7bbf3f
1 file changed