patch: MIPS32 support

[Anders Norlander]

Hi,

this patch adds support for the MIPS32 standard to gas/opcodes/bfd.
I'd appreciate feedback from people with experience of the mips code
in binutils.

MIPS32 builds on ISA 1&2 + some extensions and enhancements from
higher ISAs.

The only MIPS32 processors I know of are the 4K cores (4Kc, 4Km, 4Kp).
Since these processors don't have a number like the classic MIPS processors.
Internally I used 4750 to indicate these processors, I came up with that
number by putting together 4 + ascii value of 'K' + '0' (4 75 0). Suggestions
for a better solution would be appreciated.

There might be better names for things like 'bfd_mach_mips4K', perhaps
bfd_mach_mips32?

Feedback welcome.

Regards,
Anders