drm/amd/powerplay: report correct AC/DC event based on ctxid V2

'ctxid' is used to distinguish different events raised from SMC.
0x3 and 0x4 are for AC and DC power mode.

V2: update the way to retrieve the ctxid and change the log level
    to debug

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