MIPS: Fix the declaration conflict of mm_isBranchInstr()

mm_isBranchInstr() is declared both in branch.h and in fpu_emulator.h
but the two declarations are conflict. If both of them are included by
a same file, they will cause a build error:

./arch/mips/include/asm/branch.h:33:19: error: static declaration of 'mm_isBranchInstr' follows non-static declaration
 static inline int mm_isBranchInstr(struct pt_regs *regs,
                   ^
./arch/mips/include/asm/fpu_emulator.h:177:5: note: previous declaration of 'mm_isBranchInstr' was here
 int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,

Fix this error by removing both isBranchInstr() and mm_isBranchInstr()
in fpu_emulator.h, and declaring both of them in branch.h.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>