[PATCH][gold] Mips: Add support for MIPS R6.

[Vladimir Radosavljevic]

> But you'll still print two separate error messages, one that just says
> just "PC-relative load from unaligned address", and a second with
> details that says "relocation cannot be applied". How about simply
> returning a new STATUS_PCREL_UNALIGNED code, then print a single error
> message at the end of relocate::relocate() that's more to the point?
> You can save STATUS_BAD_RELOC for the generic "unexpected opcode while
> processing relocation".

Done. 
Thanks for review!

Regards,
Vladimir