mmc: USB SD Host Controller (USHC) driver

Add a driver for USB SD Host Controller devices.  These devices are
Cypress Astoria chips with firmware compliant with issue 2 of CSR's USHC
specification.

[cjb: adapt to block layer deprecation of max_{hw,phys}_segs]
Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/Kconfig

@@ -451,3 +451,17 @@ config MMC_JZ4740
 	  SoCs.
 	  If you have a board based on such a SoC and with a SD/MMC slot,
 	  say Y or M here.
+
+config MMC_USHC
+	tristate "USB SD Host Controller (USHC) support"
+	depends on USB
+	help
+	  This selects support for USB SD Host Controllers based on
+	  the Cypress Astoria chip with firmware compliant with CSR's
+	  USB SD Host Controller specification (CS-118793-SP).
+
+	  CSR boards with this device include: USB<>SDIO (M1985v2),
+	  and Ultrasira.
+
+	  Note: These controllers only support SDIO cards and do not
+	  support MMC or SD memory cards.

drivers/mmc/host/Makefile

@@ -36,6 +36,7 @@ obj-$(CONFIG_MMC_VIA_SDMMC)	+= via-sdmmc.o
 obj-$(CONFIG_SDH_BFIN)		+= bfin_sdh.o
 obj-$(CONFIG_MMC_SH_MMCIF)	+= sh_mmcif.o
 obj-$(CONFIG_MMC_JZ4740)	+= jz4740_mmc.o
+obj-$(CONFIG_MMC_USHC)		+= ushc.o
 
 obj-$(CONFIG_MMC_SDHCI_PLTFM)			+= sdhci-platform.o
 sdhci-platform-y				:= sdhci-pltfm.o