Add and correct MIPS relocation types

The correct names for R_MIPS_GOT_HI16 and R_MIPS_GOT_LO16 have a _
after GOT. The nonstandard names (R_MIPS_GOTHI16, R_MIPS_GOTLO16) in the
FreeBSD elf_common.h header also had incorrect values and were not used
in the tree, so just remove them.

Add other MIPS relocation types found in FreeBSD/mips64 object files.

Reviewed by: imp, jmallett
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D6561