Add MES_v12 header definition for gfx12

v2: Modify SET_SHADER_DEBUGGER to match mes_v11 definition. This doesn't
change the structure layout

v3: Removed unncessary comment and spaces
Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>