ARM: sa1100/pxa: fix MTD_XIP build

ARM: sa1100/pxa: fix MTD_XIP build

In commit 3169663ac5902 "ARM: sa11x0/pxa: convert OS timer registers
to IOMEM", the definition of the OSCR macro was changed to be an
__iomem pointer, but the same register is also used by the XIP
code. This patch does the corresponding change here as well.

On PXA, the IRQ register definitions were removed even earlier, in
commit 5d284e353eb1 ("ARM: pxa: avoid accessing interrupt registers
directly"). This patch unfortunately brings some of that back. An
earlier version of my patch moved the code into an external function,
which could not work for CONFIG_XIP_KERNEL+CONFIG_MTD_XIP, so this
restores something close to the original code.

Link: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-March/241716.html
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>