Fix the vt(4) framebuffer driver on RPi 2.

Use the BCM2835_MBOX_CHAN_PROP mbox channel to setup the framebuffer,
remove DMA code (its now done in bcm2835_mbox.c).

Also adjust the color palette when bcm2708_fb.fbswap is set. The
firmware used on RPi 2 uses this mode.

Tested on: RPi-B and RPi 2 with 16, 24 and 32bpp
Note: The 32bpp mode on RPi-B has the red and blue swapped, this

		is a know problem (not a driver problem).