drm/amd/display: remove duplicated edp relink to fastboot

[Why&How]
enable_accelerated_mode function is fully to check
whether fastboot support or not.
It is no longer to disable_vbios_mode_if_required.

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Chiawen Huang <chiawen.huang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>