mmc: Move core functions to subdir

Create a "core" subdirectory to house the central bus handling
functions.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/drivers/mmc/Makefile b/drivers/mmc/Makefile
index 4d2bdfe..9979f5e 100644
--- a/drivers/mmc/Makefile
+++ b/drivers/mmc/Makefile
@@ -6,12 +6,7 @@
 	EXTRA_CFLAGS		+= -DDEBUG
 endif
 
-#
-# Core
-#
-obj-$(CONFIG_MMC)		+= mmc_core.o
-mmc_core-y			:= mmc.o mmc_sysfs.o
-
+obj-$(CONFIG_MMC)		+= core/
 obj-$(CONFIG_MMC)		+= card/
 obj-$(CONFIG_MMC)		+= host/