[ARM GlobalISel] Support floating point for Thumb2

This is exactly the same as arm mode, so for the instruction selector
tests we just extract them to a new file and run with the same checks
for both arm and thumb mode.

For the legalizer we need to update the tests for soft float a bit, but
only because BL and tBL are slightly different. We could be pedantic and
check that we get a well-formed BL for arm mode and a tBL for thumb, but
for the purposes of the legalizer test it's sufficient to just skip over
the predicate operands in the checks. Also note that we have the
pedantic checks in the divmod test, so we're covered.

llvm-svn: 354665