MFC r323108, r323125, r326047-r326049

r323108:
Add efimedia attribute for all GPT partitions.

r323125:
The hard drive media device path contains the size of the partition,
not its end. This makes the GEOM efimedia attribute match the
FreeBSD:Boot1Device environment variable now.

r326047:
Implement efi media tagging for MBR partitioning types.

r326048:
Remove trailing whitespace (one I just introduced and a bunch of
others in the same directory).

r326049:
While the EFI spec allows numbers to be in many forms, libefivar
produces hex numbers for the dsn. Since that come is from EDK2, change
this for symmetry, by generating the dsn as a hex number.

[Missed as part of the efivar/efibootmgr MFCs]

Reported by: Oliver Pinter <oliver.pinter@hardenedbsd.org>