ARM: pxa: stop using mach/bitfield.h

There are two identical copies of mach/bitfield.h, one for
mach-sa1100 and one for mach-pxa. The pxafb driver only
makes use of two macros, which can be trivially open-coded
in the header.

Cc: dri-devel@lists.freedesktop.org
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>