Avoid resetting the UseSoftFloat and FloatABIType on the TargetMachine
Options struct and move the comment to inMips16HardFloat. Use the
fact that we now know whether or not we cared about soft float to
set the libcalls.
Accordingly rename mipsSEUsesSoftFloat to abiUsesSoftFloat and
propagate since it's no longer CPU specific.
Reset the Subtarget in the AsmPrinter for each machine function
and add explanatory comment about dual initialization. Fix
use of the Subtarget to grab the information off of the target machine.