drm/amd/powerplay: disable uclk dpm by default

[why]
The uclk dpm feature is not supported by some certain navi10
board like 18202, while supported by some board like 18201.
It causes modprobe failure on 18202 board.

[how]
Disabled this feature by default, it can be enabled by module parameter
uclk_dpm_support=1.

Reviewed-by: Jack Xiao <Jack.Xiao@amd.com>
Signed-off-by: tiancyin <tianci.yin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>