Use string_value to see if the variable is set for gfx_default_rocblas()

[ahsan-ca]

Use string_value instead of enabled to see if the variable is set for gfx_default_rocblas().

This fixes an issue where we always default to rocblas for gfx90a, even when MIGRAPHX_SET_GEMM_PROVIDER is set to hipblaslt.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3937   +/-   ##
========================================
  Coverage    92.41%   92.41%           
========================================
  Files          522      522           
  Lines        22532    22542   +10     
========================================
+ Hits         20822    20832   +10     
  Misses        1710     1710           

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[ahsan-ca]

Jenkins run has passed: http://micimaster.amd.com/blue/organizations/jenkins/AMDMIGraphX/detail/PR-3937/1/pipeline Not sure why that is not being reported in the PR. Performance test failure is unrelated to the PR, its occurring on other PRs as well:

Traceback (most recent call last):
  File "/usr/share/migraphx/AMDMIGraphX_runners/GPU942F_1/_work/AMDMIGraphX/AMDMIGraphX/benchmark-utils/scripts/comment.py", line 106, in <module>
    os.chdir(get_last_nth(x,path))
  File "/usr/share/migraphx/AMDMIGraphX_runners/GPU942F_1/_work/AMDMIGraphX/AMDMIGraphX/benchmark-utils/scripts/comment.py", line 29, in get_last_nth
    raise IndexError(f"Not enough matching paths in {path}, expexted {n}, found {len(new_path)}")
IndexError: Not enough matching paths in /usr/share/migraphx/AMD/test-results, expexted 10, found 9