mount-usb switched to dynamic USB device detection a while back,
so eliminate instances of CONFIG_BOOT_USB_DEV, and derive the
mounted USB device from /etc/mtab in the one place where it's
actually needed (usb-scan). Clean up areas around calls to
mount-usb for clarity/readability.
Addresses issue #673
Test: Build Librem 13v4, boot ISO file on USB
Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>
* Add support for the Lenovo ThinkPad T420 and X220.
* Fix the autodetection of ifdtool and me_cleaner.
* Enable FBWhiptail mode for X220 and T420
* Decreased CBFS size to fix 50 seconds boot delay problems