ARM: bcm2835: Switch BCM2835 to sdhci-iproc.c for MMC

This approximately triples write performance for the SD card.  My card
is too full of important data to collect very reliable numbers, but I
see 271.361% +/- 166.742% improvement (n=3 before, 6 after), for 'dd
if=/dev/zero of=/boot/asdf bs=1M count=3 oflag=dsync,direct'.  Read
performance appears to be unaffected.
Signed-off-by: NEric Anholt <eric@anholt.net>
Acked-by: NStephen Warren <swarren@wwwdotorg.org>

arch/arm/configs/bcm2835_defconfig

@@ -87,7 +87,7 @@ CONFIG_USB_DWC2=y
 CONFIG_MMC=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_PLTFM=y
-CONFIG_MMC_SDHCI_BCM2835=y
+CONFIG_MMC_SDHCI_IPROC=y
 CONFIG_NEW_LEDS=y
 CONFIG_LEDS_CLASS=y
 CONFIG_LEDS_GPIO=y