ARM: pxa: fix colibri build

The colibri_ohci_init function performs a register access through
the io_p2v() macro, which requires the IOMEM macro to be defined.

By explicitly including the asm/io.h header file that contains
this macro, we avoid the build error:

arch/arm/mach-pxa/colibri-evalboard.c: In function 'colibri_ohci_init':
arch/arm/mach-pxa/colibri-evalboard.c:68:2: error: implicit declaration of function 'IOMEM' [-Werror=implicit-function-declaration]
  UP2OCR = UP2OCR_HXS | UP2OCR_HXOE | UP2OCR_DPPDE | UP2OCR_DMPDE;

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Eric Miao <eric.y.miao@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Daniel Mack <zonque@gmail.com>