[AArch64] Small rejig of fmax tests, NFCI.

[AArch64] Small rejig of fmax tests, NFCI.

These tests relied on -enable-no-nans-fp-math, whereas soon they'll take their no-nans hint
from the FCMP instruction itself, so split the no-nans stuff out into its own test.

Also do a slight rejig of instruction order. The old FMIN/MAX backend matching had to deal with looking through casts, which it never did particularly well. Now, instcombine will recognize such patterns and canonicalize the cast outside the select. So modify the test inputs to assume that instcombine has already run.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244913 91177308-0d34-0410-b5e6-96231b3b80d8