Split part_type into separate types 'mbr_type' and 'gpt_type',

Split part_type into separate types 'mbr_type' and 'gpt_type',
shrinking static data demands. Split PRT_printall() into
PRT_print_mbrtypes() and PRT_print_gpttypes() to eliminate
pointless 'pseudo' MBR partition types and pointless display of
MBR partition types with no associated GPT GUIDs.

Eases future MBR and GPT partition type editing improvements.

ok kettenis@