[AMDGPU] Add tests for v_sat_pk_u8_i16 codegen (#122438)

Preparation for #121124 

This PR provides tests added into
[PR](#121124) that add
selection patterns for instruction `v_sat_pk`, in order to specify the
change of the tests before and after the commit.

Pre-commit tests PR for #121124 : Add selection patterns for instruction
`v_sat_pk`

Author: Shoreshen