Support booting from non zero MMC device numbers
Support booting from non zero MMC device numbers

On ARM platform read kernel from device passed in from u-boot
instead of hardcoding it to 0

BUG=none
TEST=emerged on seaboard, booted from SD card and emmc

Change-Id: Ia4506ed9f85d94eb37a9ac57430e1490d106c403

Review URL: http://codereview.chromium.org/5612008
Patch from Allen Martin <amartin@nvidia.com>.

crawford/scripts,sigma/coreos-scripts,glevand/coreos--scripts,marineam/coreos-scripts,smilart/scripts,BugRoger/scripts,bcwaldon/coreos-scripts,bcwaldon/coreos-scripts,fivethreeo/scripts,mjg59/scripts,fivethreeo/scripts,andrejro/coreos--scripts,mischief/scripts,endocode/scripts,nicescale/scripts,fivethreeo/scripts,trnubo/scripts,smilart/scripts,marineam/coreos-scripts,zhang0137/scripts,sigma/coreos-scripts,vmware/coreos-scripts,endocode/scripts,andrejro/coreos--scripts,crawford/scripts,coreos/scripts,gtank/scripts,trnubo/scripts,crawford/scripts,gtank/scripts,bcwaldon/coreos-scripts,glevand/coreos--scripts,endocode/scripts,trnubo/scripts,vmware/coreos-scripts,mjg59/scripts,mjg59/scripts,zhang0137/scripts,nicescale/scripts,zhang0137/scripts,andrejro/coreos--scripts,mischief/scripts,vmware/coreos-scripts,BugRoger/scripts,BugRoger/scripts,sigma/coreos-scripts,smilart/scripts,nicescale/scripts,mischief/scripts,gtank/scripts,coreos/scripts,marineam/coreos-scripts