drm/amd/powerplay: add specific changes for VEGAM in smu7_hwmgr.c

VEGAM specific changes for smu7:
1. add avfs control.
2. add a smc message defferent as smu7.
3. don't switch mc arb memory timing.
4. update LCAC_MC0/1_CNTL value.

Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>