[LLDB][MIPS] Handle PIC calling convention for MIPS64

    
    SUMMARY:
    This patch sets up register r25 with the address of function to be called in PrepareTrivialCall().
    This is required as per MIPS PIC calling convention.
    
    Reviewers: clayborg
    Subscribers: mohit.bhakkad, sagar, jaydeep, lldb-commits
    Differential Revision: http://reviews.llvm.org/D16046

llvm-svn: 257441