cros_bundle_firmware: Implement the boot source machine param
This allows us to select the SPL boot source.
BUG=chromium-os:28394
TEST=manual:
$ cros_bundle_firmware -b daisy -w sd: -B usb
See that it boots from SD, then goes into USB download mode instead
of booting U-Boot from SD
$ sudo smdk-usbdl -a 0x43e00000 -f out/u-boot-from-image.bin
See that it boots the U-Boot thus downloaded
Change-Id: I546e72a86560e0ed832f1c0d193c749ebadf9ecc
Reviewed-on: https://gerrit.chromium.org/gerrit/23406
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Ready: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
4 files changed
