grub.cfg patch from shmalebx9: reverse search order for encrypted partitions

Also, when a cryptomount is successful, break from the loop and boot from that.
In most cases, this will work just fine, and this change improves the boot
speed in the vast majority of cases.

From <https://notabug.org/libreboot/lbmk/issues/53>

This is based on commit 5767489cadc4a9a1f2e7bffe03457e29e1c9a101 from
https://github.com/shmalebx9/Bleeding-Libreboot/