[patch][x86] skylake costs

[Koval, Julia]

Hi, this patch introduces separate cost model for skylake-avx512. Ok for trunk?

gcc/
        * config/i386/i386.c (processor_target_table): Add skylake_cost for
        skylake-avx512.
        * config/i386/x86-tune-costs.h (skylake_memcpy, skylake_memset,
        skylake_cost): New.
Thanks,
Julia

0001-cost-model.patch
Description: 0001-cost-model.patch