drm/amd/pm: add the callback to get vbios bootup values for vangogh

This patch is to add the callback to get vbios bootup values for
vangogh, it will get the bootup values of gfxclk, mclk, socclk and so
on.

Signed-off-by: Xiaojian Du <Xiaojian.Du@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>