[mips] Use AltOrders to prevent using odd FP-registers

To disable using of odd floating-point registers (O32 ABI and
-mno-odd-spreg command line option) such registers and their
super-registers added to the set of reserved registers. In general, it
works. But there is at least one problem - in case of enabled machine
verifier pass some floating-point tests failed because live ranges of
register units that are reserved is not empty and verification pass
failed with "Live segment doesn't end at a valid instruction" error
message.

There is D35985 patch which tries to solve the problem by explicit
removing of register units. This solution did not get approval.

I would like to use another approach for prevent using odd floating
point registers - define `AltOrders` and `AltOrderSelect` for MIPS
floating point register classes. Such `AltOrders` contains reduced set
of registers. At first glance, such solution does not break any test
cases and allows enabling machine instruction verification for all MIPS
test cases.

Differential Revision: http://reviews.llvm.org/D59799

llvm-svn: 357472

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