mfd: Add support for STMPE SPI interface

Few STMPE controller can have register interface over SPI or I2C. Current
implementation only supports I2C.

This patch adds support for SPI interface for accessing STMPE's address space.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 7bc5581..06766ec 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -258,7 +258,7 @@
 
 config MFD_STMPE
 	bool "Support STMicroelectronics STMPE"
-	depends on I2C=y && GENERIC_HARDIRQS
+	depends on (I2C=y || SPI_MASTER=y) && GENERIC_HARDIRQS
 	select MFD_CORE
 	help
 	  Support for the STMPE family of I/O Expanders from
@@ -288,6 +288,12 @@
 	default y
 	help
 	  This is used to enable I2C interface of STMPE
+
+config STMPE_SPI
+	bool "STMPE SPI Inteface"
+	depends on SPI_MASTER
+	help
+	  This is used to enable SPI interface of STMPE
 endmenu
 
 config MFD_TC3589X