drm/i915/fbdev: Restore physical addresses for fb_mmap()

drm/i915/fbdev: Restore physical addresses for fb_mmap()

fbdev uses the physical address of our framebuffer for its fb_mmap()
routine. While we need to adapt this address for the new io BAR, we have
to fix v5.4 first! The simplest fix is to restore the smem back to v5.3
and we will then probably have to implement our fbops->fb_mmap() callback
to handle local memory.

Reported-by: Neil MacLeod <freedesktop@nmacleod.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112256
Fixes: c3adcfc2c3d2 ("drm/i915: Disregard drm_mode_config.fb_base")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Tested-by: Neil MacLeod <freedesktop@nmacleod.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191113180633.3947-1-chris@chris-wilson.co.uk