Improve sysctl(8) pretty printing of some structures.

S_vmtotal:
Use unsigned format to print unsigned memory counters from struct
vmtotal.
Remove unneeded cast, style locals declarations.

S_efi_map:
Make printing of the memory regions descriptions less MD by
using uintmax_t formats.

Noted by and discussed with: bde
Sponsored by: The FreeBSD Foundation
MFC after: 1 week