propose mips32r2 for mips{,el} and mips64r2 for mips64el in Debian

hi, folks,

As all of us may know that the current ISA used for mips{,el} in
Debian is MIPS II,
which is quite, quite old, and make all newer devices running in a slow speed.

As the step 0, we have already enable FPXX and no-odd-spreg in gcc-5 by default.
Build with FPXX and no-odd-spreg, the binary can compatible with both old mips2
architecture and the future FP64 architecture (aka, with 32 64-bit FPR)[1].

The next step, we will build gcc-5 with the default ISA with mips32r2/mips64r2.

Who will be effect:
1. Who use old machines, Loongson-2E/F included.
    They will cannot use the new Debian release.
2. Who use new machines, Loongson-3, OcteonIII, CI20 etc included.
    They will get better performance.
3. Who use Loongson-3.
    They may meet some Loongson-3 bugs. for FPU.


[1].https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking