mips: add assembler flags for mips32r2 ISA and mhard-float

For some compilers ISA older than mips32r2 is set as default.
 Because of them assembler flag "-mips32r2" needs to be added
 for CPUs that support mips32r2 ISA in part of configure script
 where ISA capabilities are checked.
"-mhard-float" assembler flag is also added for CPUs that have FPU.

Signed-off-by: Nedeljko Babic <nbabic@mips.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>