drm/amd/display: Set vsc pack revision when DPCD revision is >= 1.2

drm/amd/display: Set vsc pack revision when DPCD revision is >= 1.2

BugLink: http://bugs.launchpad.net/bugs/1786352
[ Upstream commit 3b94a4007dcfd4ac5780cd3d8a2d99979c966073 ]

Brightness couldn't change when booting up in DC mode.
It was because "psr_enabled" flag was not set to true before
setting vsc packet revision, causing packet rev setup was skipped.
Now instead of checking the psr flag, it checks if the DPCD_REV >= 1.2
and set the vsc packet revision.

Signed-off-by: Tao <xtao@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>