[mips] Correct .MIPS.abiflags fp_abi field for -mfpxx and without .module

Summary: Previously all the test cases set it after initialization with '.module fp=xx'.

Differential Revision: http://reviews.llvm.org/D4489


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213071 91177308-0d34-0410-b5e6-96231b3b80d8