x86-64: Improve evex512 version of strlen functions

This patch improves following functionality
- Replace VPCMP with VPCMPEQ.
- Replace page cross check logic with sall.
- Remove extra lea from align_more.
- Remove uncondition loop jump.
- Use bsf to check max length in first vector.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>