drm/radeon: update radeon_atom_is_voltage_gpio() for SI

SI uses a new atom table.  Required for DPM on SI.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/btc_dpm.c
Simple merge

diff --cc drivers/gpu/drm/radeon/cypress_dpm.c
Simple merge

diff --cc drivers/gpu/drm/radeon/ni_dpm.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_atombios.c
Simple merge

diff --cc drivers/gpu/drm/radeon/rv6xx_dpm.c
Simple merge

diff --cc drivers/gpu/drm/radeon/rv770_dpm.c
Simple merge