baytrail: initialize eMMC device

The eMMC device is initialized as version 4.5 with HS200 speeds.

BUG=chrome-os-partner:23966
BRANCH=None
TEST=Built and booted rambi to login screen off of eMMC device.

Change-Id: I686c6136005fcb2587b939ddea293f4398df9868
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/176536
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/4967
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/soc/intel/baytrail/Makefile.inc

@@ -40,6 +40,7 @@ ramstage-y += sata.c
 ramstage-y += acpi.c
 ramstage-y += lpe.c
 ramstage-y += scc.c
+ramstage-y += emmc.c
 
 # Remove as ramstage gets fleshed out
 ramstage-y += placeholders.c