loader: Replace EFI part devices.
Rewrite EFI part device interface to present disk devices in more
user friendly way.
We keep list of three types of devices: floppy, cd and disk, the
visible names: fdX: cdX: and diskX:
Use common/disk.c and common/part.c interfaces to manage the
partitioning.
The lsdev -l will additionally list the device path.
Reviewed by: imp, allanjude
Approved by: imp (mentor), allanjude (mentor)
Differential Revision: https://reviews.freebsd.org/D8581