Optimizing sgemm rd kernels on zen3 (flame#293)

Fixing some inefficiencies on the zen (AVX2) SUP RD kernel for SGEMM.
After performing the iteration for the 8 loop, the next loop that was being performed was the 1 loop for the k-direction.
This caused a lot of unnecessary iterations when the remainder of k < 8.
This has been fixed by introducing masked operations for k < 8
When remainder of k == 1, we handle this with the original non-masked code (with a branch) as the masked code introduces more penalty because of the masking operation.
There were also some unnecessary instructions in the zen4 kernels which have been removed.

AMD-Internal: https://amd.atlassian.net/browse/CPUPL-7775
Co-authored-by: rohrayan@amd.com

Author: rohrayan