[AArch64][llvm] Codegen for 16/32/64-bit floating-point atomicrmw fminimum/faximum (#137703)
Codegen for AArch64 16/32/64-bit floating-point atomic read-modify-write
operations (`atomicrmw {fmaximum,fminimum}`) using LD{B}FMAX and
LD{B}FMIN atomic instructions.