drm/amd/display: turn on symclk for dio virtual stream in dpms sequence

drm/amd/display: turn on symclk for dio virtual stream in dpms sequence

[why]
In order to support glitchless display clock ramping for virtual stream,
we must
turn on symclk for stream encoder. The code will power on phy and enable
symclk
for dio encoder during virtual stream dpms sequence.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>