build(rss): introduce rss_comms.mk makefile

Provide a new makefile as a convenience for platform makefiles to pull
in the list of source files and headers for the RSS communication
driver.

Change-Id: I188a1a8f4e77318cdc87c3155b280090c46ce813
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
1 file changed