lxfb: clean up final bits of df_regs

Finally drop the last remnants of df_regs, using vp_regs instead.  Also, drop
panel_width and panel_height from lxfb_par; they're unused.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>