[AMDGPU][GFX12] VOP encoding and codegen - add support for v_cvt fp8/… (#78414)

…bf8 instructions

    Add VOP1, VOP1_DPP8, VOP1_DPP16, VOP3, VOP3_DPP8, VOP3_DPP16
    instructions that were supported on GFX940 (MI300):
    - V_CVT_F32_FP8
    - V_CVT_F32_BF8
    - V_CVT_PK_F32_FP8
    - V_CVT_PK_F32_BF8
    - V_CVT_PK_FP8_F32
    - V_CVT_PK_BF8_F32
    - V_CVT_SR_FP8_F32
    - V_CVT_SR_BF8_F32

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Co-authored-by: Mateja Marjanovic <mateja.marjanovic@amd.com>
Co-authored-by: Mirko Brkušanin <Mirko.Brkusanin@amd.com>