v2: change power unit to microWatt

Adust power limit through power1_cap
Get min/max power limit through power1_cap_min/power1_cap_max
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>