gpio: add MSIC gpio driver

Add gpio support for Intel MSIC chips found in Intel Medfield platforms.
MSIC supports totally 24 GPIOs with 16 low voltage and 8 high voltage pins.
Driver uses MSIC mfd interface for MSIC access.

(Updated comment to indicate why locking is actually safe)

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 8ee6d29..5169a99 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -520,4 +520,12 @@
 	help
 	  Select this option to enable GPIO driver for the TPS65910
 	  chip family.
+
+config GPIO_MSIC
+	bool "Intel MSIC mixed signal gpio support"
+	depends on MFD_INTEL_MSIC
+	help
+	  Enable support for GPIO on intel MSIC controllers found in
+	  intel MID devices
+
 endif