drm/amd/display: Reset planes that were disabled in init_pipes

drm/amd/display: Reset planes that were disabled in init_pipes

[Why]
Seamless boot tries to reuse planes that were enabled for the first
commit applied.

In the case where Raven is booting with two monitors connected and the
first commit contains two streams the screen corruption would occur
because the second stream was trying to re-use a tg and plane that
weren't previously enabled.

The state on the first commit looks something like the following:

TG0: enabled=1
TG1: enabled=0
TG2: enabled=0
TG3: enabled=0

New state: pipe=0, stream=0,    plane=0,       new_tg=0
New state: pipe=1, stream=1,    plane=1,       new_tg=1
New state: pipe=2, stream=NULL, plane=NULL,    new_tg=NULL
New state: pipe=3, stream=NULL, plane=NULL,    new_tg=NULL

Only one plane/tg is setup before we enter accelerated mode so
we really want to disabling everything but that first plane.

[How]

Check if the stream is not NULL and if the tg is enabled before
deciding whether to skip the plane disable.

Also ensure we're also disabling on the current state's pipe_ctx so
we don't overwrite the fields in the new pending state.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>