Prevented calling avx2 based bli_zgemm_ref_k1_nn code on
non-supported systems.
Changed the name of the function bli_zgemm_ref_k1_nn to bli_zgemm_4x6_avx2_k1_nn().
Changed the name of the function bli_dgemm_ref_k1_nn to bli_dgemm_8x6_avx2_k1_nn().
Thanks to Kiran Varaganti <Kiran.Varaganti@amd.com>
for identifying and helping to fix the issue.
AMD-Internal: [CPUPL-3352]
Change-Id: I02530ab197ed84c96cbad4f7dd56eedca0109c35