[ARM] 't' asm constraint should accept i32

't' constraint normally only accepts f32 operands, but for VCVT the
operands can be i32. LLVM is overly restrictive and rejects asm like:

  float foo() {
    float result;
    __asm__ __volatile__(
      "vcvt.f32.s32 %[result], %[arg1]\n"
      : [result]"=t"(result)
      : [arg1]"t"(0x01020304) );
    return result;
  }

Relax the value type for 't' constraint to either f32 or i32.

Differential Revision: https://reviews.llvm.org/D40137

llvm-svn: 318472