amlogic: Fix prefixes in the SIP/SVC code

All the SIP/SVC related code is currently the same between GXL and GXBB.
Rename function names and register names to avoid hardcoding the GXBB
prefix.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: I7e58ab68489df8d4762663fc01fb64e6899cc8bf