Since Davinci GPIO driver is moved to support gpiolib it has to use
ARCH_NR_GPIOS (can be configured using CONFIG_ARCH_NR_GPIO Kconfig
option) configuration instead of any mach/platform specific options.
Hence, replace private DAVINCI_N_GPIO with common ARCH_NR_GPIOS. This is
safe because default value for ARCH_NR_GPIOS=256 and maximum number of
supported GPIOs for Davinci is DAVINCI_N_GPIO=144.
More over, this is one of steps to re-use Davinci GPIO driver by other
mach/platform.