video: implement a dumb framebuffer driver

A dumb frame-buffer describes a raw memory region that may be rendered
to, with the assumption that the display hardware has already been set
up to scan out from that buffer.

This is useful in cases where a bootloader exists and has set up the
display hardware, but a Linux driver doesn't yet exist for the display
hardware.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
---
Should this be merged through akpm's tree (I think many fb drivers are
these days), or if not, I could take it through the bcm2835 tree.

I ended up going with a separate FB driver:
* DRM/KMS look much more complex, and don't provide any benefit that I can
  tell for this simple driver.
* Creating a separate driver rather than adjusting offb.c to work allows a
  new clean binding to be defined, and doesn't require removing or ifdefing
  PPC-isms in offb.c.
ARM: bcm2835: add dumb framebuffer to device tree

Place a template dumb-framebuffer device into the RPi device tree. The
bootloader is expected to fill in all the parameters at boot time.
Hence, disable the device by default, so if the bootloader doesn't do
this, the device isn't activated with invalid parameters.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm235: defconfig updates for dumb framebuffer

Enable the dumb framebuffer driver, fbconsole, and VT support.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
LOCAL HACK: ARM: bcm2835: fill in dumb-framebuffer parameters

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>