drm/amd/display: Add initialitions for PLL2 clock source

[Why]
Starting from 14nm, the PLL is built into the PHY and the PLL is mapped
to PHY on 1 to 1 basis. In the code, the DP port is mapped to a PLL that was not
initialized. This causes DP to HDMI dongle to not light up the display.

[How]
Initializations added for PLL2 when creating resources.

Signed-off-by: Isabel Zhang <isabel.zhang@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>