target-mips: optimize movc*()

Optimize code generation in gen_movc*():
- Temp variables are valid up to and *including* the brcond instruction.
  Use them instead of temp local variables.
- Avoid using temporary variables to transfer values.
- Access fpu_fcr31 directly in gen_movcf_ps().

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5683 c046a42c-6fe2-441c-8c8c-71466251a162
