To help with the DC port.
v2: add missing masks, add additional registers
v3: more updates
v4: fix accidently dropped changes
v5: add missing nb pstate mask
v6: add vblank, vline masks
v7: add SCL_HORZ_FILTER_INIT regs
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>