drm/amd/display: register edp_backlight_control() for DCN301

As made mention of in commit 099303e9 ("drm/amd/display: eDP
intermittent black screen during PnP"), we need to turn off the
display's backlight before powering off an eDP display. Not doing so
will result in undefined behaviour according to the eDP spec. So, set
DCN301's edp_backlight_control() function pointer to
dce110_edp_backlight_control().

Cc: stable@vger.kernel.org
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2765


Fixes: 9c75891f ("drm/amd/display: rework recent update PHY state commit")
Suggested-by: Swapnil Patel <swapnil.patel@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>