[LLDB][MIPS] Add LinuxSignals for mips64 and change trap opcode for mips64el.

Patch by Sagar Thakur

- Added LinuxSignals for MIPS64.
- Changed software trap opcode for mips64el.

Reviewers: clayborg, tberghammer.

Subscribers: emaste, jaydeep, bhushan, mohit.bhakkad, llvm-commits.

Differential Revision: http://reviews.llvm.org/D8856

llvm-svn: 234469