mcp23s08 spi gpio expander support

Basic driver for 8-bit SPI based MCP23S08 GPIO expander, without support for
IRQs or the shared chipselect mechanism.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Eric Miao <eric.miao@marvell.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ben Gardner <bgardner@wabtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpio/Kconfig

@@ -52,4 +52,11 @@ config GPIO_PCF857X
 
 comment "SPI GPIO expanders:"
 
+config GPIO_MCP23S08
+	tristate "Microchip MCP23S08 I/O expander"
+	depends on SPI_MASTER
+	help
+	  SPI driver for Microchip MCP23S08 I/O expander.  This provides
+	  a GPIO interface supporting inputs and outputs.
+
 endmenu