pxafb: Add support for other palette formats

This patch adds support for the other three palette formats possible with
the PXA LCD controller. This is required on boards where an LCD is connected
with all its 18 bits. With this patch, it's possible to use an 8-bit mode
with 18-bit palette entries. This used to be possible in 2.4 kernels but
disappeared in 2.6. With current kernels, you can only get wrong colours
out of an LCD connected this way.

Users can choose the palette format by doing something like this
in their board definition:

static struct pxafb_mach_info my_fb_info = {
        [...]
        .lccr3          = LCCR3_OutEnH | LCCR3_PixFlEdg | LCCR3_PDFOR_3,
        .lccr4          = LCCR4_PAL_FOR_2,
        [...]
};

Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>