fix(tc): unify TC ROM start addresses

Because RSS now does not map the header into the TC2 ROM, it is no
longer necessary to have the code start at 0x1000, so unify with other
TC platforms at 0x0.

Change-Id: I7ec34bb814865ba39678f4da0412294d4679052d
Signed-off-by: Raef Coles <raef.coles@arm.com>