refactor(fiptool): change all occurrences of RSS to RSE

Changes all occurrences of "RSS" and "rss" in the code and build files
to "RSE" and "rse".

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Change-Id: I8982c203375250d6c709a26f33fb88673d69da50
1 file changed