mfd: Separate out STMPE controller and interface specific code

Few STMPE controller can have register interface over SPI or I2C. Current
implementation only supports I2C and all code is present in a single file
stmpe.c. It would be better to separate out I2C interface specific code from
controller specific code. Later SPI specific code can be added in a separate
file.

This patch separates out I2C and controller specific code into separate files,
making stmpe.c independent of I2C.

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/Makefile b/drivers/mfd/Makefile
index b2292eb..5eb90a7 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -16,6 +16,7 @@
 obj-$(CONFIG_MFD_TI_SSP)	+= ti-ssp.o
 
 obj-$(CONFIG_MFD_STMPE)		+= stmpe.o
+obj-$(CONFIG_STMPE_I2C)		+= stmpe-i2c.o
 obj-$(CONFIG_MFD_TC3589X)	+= tc3589x.o
 obj-$(CONFIG_MFD_T7L66XB)	+= t7l66xb.o tmio_core.o
 obj-$(CONFIG_MFD_TC6387XB)	+= tc6387xb.o tmio_core.o