[ARM] Preserve fpu behaviour for '-crypto'
This patch restores the behaviour that -fpu overwrites the
architecture obtained from -march or -mcpu flags, not enforcing to
disable 'crypto' if march=armv7 and mfpu=neon-fp-armv8.
However, it does warn that 'crypto' is ignored when passing
Reviewers: peter.smith, labrinea
Reviewed By: peter.smith
Subscribers: nickdesaulniers, kristof.beyls, dmgreen, cfe-commits, krisb
Differential Revision: https://reviews.llvm.org/D67608