drm/amd/amdgpu: Update read_sensor calls to have size parameter (v3)

This update allows sensors to return more than 1 value and
indicates to the caller how many bytes are written.

The debugfs interface has been updated to handle reading all
of the values.  Simply seek to the enum value (multiplied
by 4) and then read as many bytes as the sensor provides.

(v2):  Don't set size to 4 before reading GPU_POWER
(v3): agd: rebase

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>