gpio: Add GPIO support for Broadcom STB SoCs

This adds support for the GPIO IP "UPG GIO" used on
Broadcom STB SoCs (BCM7XXX and some others). Uses
basic_mmio_gpio to instantiate a gpio_chip for each bank.
The driver assumes that it handles the base set of GPIOs
on the system and that it can start its numbering sequence
from 0, so any GPIO expanders used with it must dynamically
assign GPIO numbers after this driver has finished
registering its GPIOs.

Does not implement the interrupt-controller portion yet,
will be done in a future commit.

v2:
- change include to use <linux/gpio/driver.h> instead of
  <linux/gpio.h>
- get rid of unnecessary imask member in struct bank
- rename GPIO_PER_BANK -> MAX_GPIO_PER_BANK
- always have 32 GPIOs per bank and add 'width' member in
  struct bank to hold actual number of GPIOs in use
- mark of_match table as const

List-usage-fixed-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -126,6 +126,14 @@ config GPIO_BCM_KONA
 	help
 	  Turn on GPIO support for Broadcom "Kona" chips.
 
+config GPIO_BRCMSTB
+	tristate "BRCMSTB GPIO support"
+	default y if ARCH_BRCMSTB
+	depends on OF_GPIO && (ARCH_BRCMSTB || COMPILE_TEST)
+	select GPIO_GENERIC
+	help
+	  Say yes here to enable GPIO support for Broadcom STB (BCM7XXX) SoCs.
+
 config GPIO_CLPS711X
 	tristate "CLPS711X GPIO support"
 	depends on ARCH_CLPS711X || COMPILE_TEST