[Why]
For fastboot, Bios will light up eDP before SW driver is loaded. SW
driver will check if eDP is lit by bios through reading the
BIOS_SCRATCH_3 register. If lit, SW driver will not power down eDP
power and phy to save time.

Definition of BIOS_SCRATCH_3 are missing for pre-raven asic. This
causes eDP fast boot to not work property. For some eDP panels, even
if dp tx sends NoVideoStream_flag =1 and dpcd 0x600=2, eDP rx may not
handle properly. This may cause a short flash on screen.

[How] Add definition of BIOS_SCRATCH_3 for all asic
Signed-off-by: hersen wu <hersenxs.wu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Yongqiang Sun <yongqiang.sun@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>