drm/amd/display: do not wait for mpc idle if tg is disabled

drm/amd/display: do not wait for mpc idle if tg is disabled

[Why]
When booting, the driver waits for the MPC idle bit to be set as part of
pipe initialization. However, on some systems this occurs before OTG is
enabled, and since the MPC idle bit won't be set until the vupdate
signal occurs (which requires OTG to be enabled), this never happens and
the wait times out. This can add hundreds of milliseconds to the boot
time.

[How]
Do not wait for mpc idle if tg is disabled

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Josip Pavic <Josip.Pavic@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>