ARM: rpi_b: enable SD controller, add related env/cmds

Enable the SD controller driver for the Raspberry Pi. Enable a number
of useful MMC, partition, and filesystem-related commands. Set up the
environment to provide standard locations for loading a kernel, DTB,
etc. Provide a boot command that loads and executes boot.scr.uimg from
the SD card; this is written considering future extensibilty to USB
storage.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
diff --git a/board/raspberrypi/rpi_b/rpi_b.c b/board/raspberrypi/rpi_b/rpi_b.c
index 3c654a1..6b3e095 100644
--- a/board/raspberrypi/rpi_b/rpi_b.c
+++ b/board/raspberrypi/rpi_b/rpi_b.c
@@ -16,6 +16,7 @@
 
 #include <common.h>
 #include <asm/arch/mbox.h>
+#include <asm/arch/sdhci.h>
 #include <asm/global_data.h>
 
 DECLARE_GLOBAL_DATA_PTR;
@@ -26,6 +27,12 @@
 	u32 end_tag;
 };
 
+struct msg_get_clock_rate {
+	struct bcm2835_mbox_hdr hdr;
+	struct bcm2835_mbox_tag_get_clock_rate get_clock_rate;
+	u32 end_tag;
+};
+
 int dram_init(void)
 {
 	ALLOC_ALIGN_BUFFER(struct msg_get_arm_mem, msg, 1, 16);
@@ -51,3 +58,22 @@
 
 	return 0;
 }
+
+int board_mmc_init(void)
+{
+	ALLOC_ALIGN_BUFFER(struct msg_get_clock_rate, msg_clk, 1, 16);
+	int ret;
+
+	BCM2835_MBOX_INIT_HDR(msg_clk);
+	BCM2835_MBOX_INIT_TAG(&msg_clk->get_clock_rate, GET_CLOCK_RATE);
+	msg_clk->get_clock_rate.body.req.clock_id = BCM2835_MBOX_CLOCK_ID_EMMC;
+
+	ret = bcm2835_mbox_call_prop(BCM2835_MBOX_PROP_CHAN, &msg_clk->hdr);
+	if (ret) {
+		printf("bcm2835: Could not query eMMC clock rate\n");
+		return -1;
+	}
+
+	return bcm2835_sdhci_init(BCM2835_SDHCI_BASE,
+				  msg_clk->get_clock_rate.body.resp.rate_hz);
+}