Eliminated arch-specific mmc header requirement

The current MMC infrastructure relies on the existence of an
arch-specific header file.  This isn't necessary, and a couple
drivers were forced to implement dummy files to meet this requirement.
Instead, we move the stuff in those header files into a more appropriate
place, and eliminate the stubs and the #include of asm/arch/mmc.h

Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/cpu/pxa/mmc.c b/cpu/pxa/mmc.c
index 7199e89..8f5277e 100644
--- a/cpu/pxa/mmc.c
+++ b/cpu/pxa/mmc.c
@@ -28,6 +28,8 @@
 #include <asm/arch/hardware.h>
 #include <part.h>
 
+#include "mmc.h"
+
 #ifdef CONFIG_MMC
 
 extern int fat_register_device(block_dev_desc_t * dev_desc, int part_no);