ARM: OMAP4: Fix NULL pointer dereference crash.

ARM: OMAP4: Fix NULL pointer dereference crash.

After the patch series "[PATCH 00/14] OMAP PM fixes for .31-rc"
merge in 2.6.31-rc5, the kernel crashed during boot on OMAP4430.
This patch fixes it by adding UART4 support and related code.
Without this patch omap_serial_init() would produce " NULL pointer
dereference" and kernel crashes in the bootup on OMAP4430 platform.

Some more info on the merge issue can be found here.
More info- http://lkml.org/lkml/2009/8/20/192

Note: While merging this patch,"IO_ADDRESS" needs to be changed
to "OMAP2_IO_ADDRESS" if the Tony's below series is already merged in.
http://www.mail-archive.com/linux-omap@vger.kernel.org/msg15072.html

Signed-off-by: Syed Rafiuddin <rafiuddin.syed@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>