FPU support

[ibara]

The PIC32MZ has an FPU. LiteBSD should support it. Then we can turn off -msoft-float in the build and have better performance.

[majenkotech]

Not all of them have it. You would have to pick-and-choose depending on which chip you have.

[ibara]

Fair enough. But that should be easy.

[sergev]

MZ-EF family has FPU, but MZ-EC does not. A proper solution is to port the FPU kernel emulation code from NetBSD (http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/mips/mips/fp.S?rev=1.46). User space binaries should assume the FPU is present (no -msoft-float option). In case there is no real FPU, every floating-point opcode will take exception, processed by the emulation code in the kernel. A performance would not be much different from the soft-float library.

The code in fp.S file looks pretty self contained. It can be debugged and verified using QEMU with tracing option enabled.