drm/fb: drop panic handling

This really doesn't seem to have much chance of working anymore,

esp for irq context, qxl at least tries to talk to the hw,
and waits for irqs, and fails.

with runtime pm and other stuff I think we should just
bail on this for now.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>