[mips] Add checks for alignment and maximum displacements for most of the
branch instructions for mips and micromips instruction sets thus avoiding
the situation of generating branches to undesired locations if offsets
cannot be encoded.

This patch also checks if a fixup cannot be applied and returns a fatal error
if that's the case.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197223 91177308-0d34-0410-b5e6-96231b3b80d8
Enabling thumb2 mode used to force support for armv6t2. Replace this
with a temporary assertion and adjust the various test cases.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197224 91177308-0d34-0410-b5e6-96231b3b80d8