mmc: add generic mmc spi driver

This patch supports mmc/sd card with spi interface. It is based on
the generic mmc framework. It works with SDHC and supports multi
blocks read/write.

The crc checksum on data packet is enabled with the def,

There is a subcomamnd "mmc_spi" to setup spi bus and cs at run time.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/drivers/mmc/Makefile b/drivers/mmc/Makefile
index 3496f0a..9aca3a2 100644
--- a/drivers/mmc/Makefile
+++ b/drivers/mmc/Makefile
@@ -31,6 +31,7 @@
 COBJS-$(CONFIG_FSL_ESDHC) += fsl_esdhc.o
 COBJS-$(CONFIG_GENERIC_MMC) += mmc.o
 COBJS-$(CONFIG_GENERIC_ATMEL_MCI) += gen_atmel_mci.o
+COBJS-$(CONFIG_MMC_SPI) += mmc_spi.o
 COBJS-$(CONFIG_MXC_MMC) += mxcmmc.o
 COBJS-$(CONFIG_OMAP3_MMC) += omap3_mmc.o
 COBJS-$(CONFIG_OMAP_HSMMC) += omap_hsmmc.o