gpio/mpc83xx_spisel_boot.c: gpio driver for SPISEL_BOOT signal

Some SoCs in the mpc83xx family, e.g. mpc8309, have a dedicated spi
chip select, SPISEL_BOOT, that is used by the boot code to boot from
flash.

This chip select will typically be used to select a SPI boot
flash. The SPISEL_BOOT signal is controlled by a single bit in the
SPI_CS register.

Implement a gpio driver for the spi chip select register. This allows a
spi driver capable of using gpios as chip select, to bind a chip select
to SPISEL_BOOT.

It may be a little odd to do this as a GPIO driver, since the signal
is neither GP or I, but it is quite convenient to present it to the
spi driver that way. The alternative it to teach mpc8xxx_spi to handle
the SPISEL_BOOT signal itself (that is how it's done in the linux
kernel, see commit 69b921acae8a)

Signed-off-by: Klaus H. Sorensen <khso@prevas.dk>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 9dd5a58..7638259 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -40,6 +40,7 @@
 obj-$(CONFIG_ALTERA_PIO)	+= altera_pio.o
 obj-$(CONFIG_MPC83XX_GPIO)	+= mpc83xx_gpio.o
 obj-$(CONFIG_MPC8XXX_GPIO)	+= mpc8xxx_gpio.o
+obj-$(CONFIG_MPC83XX_SPISEL_BOOT)	+= mpc83xx_spisel_boot.o
 obj-$(CONFIG_SH_GPIO_PFC)	+= sh_pfc.o
 obj-$(CONFIG_OMAP_GPIO)	+= omap_gpio.o
 obj-$(CONFIG_DB8500_GPIO)	+= db8500_gpio.o