Disabling planes in the middle of the modeset seuqnece does not make
sense since userspace can anyway disable planes before the modeset
even starts. So when the modeset seuqence starts the set of enabled
planes is entirely arbitrary. Trying to sprinkle the plane disabling
into the modeset sequence just means more randomness and potential
for hard to reproduce bugs.

So it makes most sense to just disable all planes first so that the
rest of the modeset sequence remains identical regardless of which
planes happen to be enabled by userspace at the time.

This reverts commit 84030adb.

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211022103304.24164-3-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>