server-fd fixes

Skip SetMaster/DropMaster for server-fd case, and add some hunks which
got missed the first time around.

Signed-off-by: Rob Clark <robdclark@gmail.com>
kms: remove fb on ScreenClose

Otherwise we'd end up with a new scanout buffer, but old fb, on the next
time around.  This way drmmode_xf86crtc_resize() realizes to create a
new fb on next server generation.

Signed-off-by: Rob Clark <robdclark@gmail.com>