fbdev: defio and Metronomefb

Implement support for the E-Ink Metronome controller.  It provides an mmapable
interface to the controller using defio support.  It was tested with a gumstix
pxa255 with Vizplex media using Xfbdev and various X clients such as xeyes,
xpdf, xloadimage.

This patch also fixes the following bug: Defio would cause a hang on write
access to the framebuffer as the page fault would be called ad-infinitum.  It
fixes fb_defio by setting the mapping to be used by page_mkclean.

Signed-off-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>