mfd: Move the mc13xxx-core spi specific code into a separate module

All spi specific code is moved into a new module. The mc13xxx struct
moves to a new local include file by necessity.

A new config choice selects the SPI bus type support and by default is
value of SPI_MASTER to remain compatible with existing configs.

Signed-off-by: Marc Reilly <marc@cpdesign.com.au>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index c4500c3..7ce5b5c 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -54,6 +54,7 @@
 obj-$(CONFIG_TWL6040_CORE)	+= twl6040-core.o twl6040-irq.o
 
 obj-$(CONFIG_MFD_MC13XXX)	+= mc13xxx-core.o
+obj-$(CONFIG_MFD_MC13XXX_SPI)	+= mc13xxx-spi.o
 
 obj-$(CONFIG_MFD_CORE)		+= mfd-core.o