[MIPS] rbtx4938: Add generic GPIO support

GPIO 0..15 are for TX4938 PIO pins, GPIO 16..18 are for FPGA-driven
chipselect signals for SPI devices.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 24661d6..823a628 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -660,6 +660,7 @@
 	select SYS_SUPPORTS_BIG_ENDIAN
 	select SYS_SUPPORTS_KGDB
 	select GENERIC_HARDIRQS_NO__DO_IRQ
+	select GENERIC_GPIO
 	help
 	  This Toshiba board is based on the TX4938 processor. Say Y here to
 	  support this machine type