ARM: sa1100/pxa: fix MTD_XIP build

ARM: sa1100/pxa: fix MTD_XIP build

In commit d72131b3ec53d "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 63a94a1b70dd ("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>