amlogic: Fix header guards

Make the header guards more generic and contextually remove the
GXBB_BL31_PLAT_PARAM_VAL value that is unused on the GXL platform.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: I842fa2e084e71280ae17b39c67877e844821a171
3 files changed