ARM: pxa: hx4700.h: include "irqs.h" for PXA_NR_BUILTIN_GPIO

hx4700 needs the same fix as in
9705e746
"ARM: pxa: fix various compilation problems"

Fix build errors. Initial one is:
/linux/arch/arm/mach-pxa/include/mach/hx4700.h:18:32: error:
 'PXA_NR_BUILTIN_GPIO' undeclared here (not in a function)
|  #define HX4700_ASIC3_GPIO_BASE PXA_NR_BUILTIN_GPIO

Cc: stable@vger.kernel.org # v3.13+
Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>