target-mips: fix MTHC1 and MFHC1 when FPU in FR=0 mode

Previous implementation presumed that FPU registers are 64-bit and are
working in 64-bit mode. This change first checks MIPS_HFLAG_F64 and if not
set, it does load/store from the odd numbered register pair.
Patch by Matthew Fortune.

Signed-off-by: Matthew Fortune <matthew.fortune@imgtec.com>
Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
