[AMDGPU] Adding the amdgpu_num_work_groups function attribute (#79035)

A new function attribute named amdgpu_num_work_groups is added. This
attribute, which consists of three integers, allows programmers to let
the compiler know the number of workgroups to be launched in each of the
three dimensions and do optimizations based on that information.

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Co-authored-by: Jun Wang <jun.wang7@amd.com>