x86-64: Add strcpy family functions with 256-bit EVEX

Update ifunc-strcpy.h to select the function optimized with 256-bit EVEX
instructions using YMM16-YMM31 registers to avoid RTM abort with usable
AVX512VL and AVX512BW since VZEROUPPER isn't needed at function exit.

(cherry picked from commit 525bc2a3)