drm/amd/display: Refactor virtual directory reorganize encoder and hwss files.

drm/amd/display: Refactor virtual directory reorganize encoder and hwss files.

[why]
Virtual encoders & hwss were grouped in a separate directory,
not aligned with dio and link component structure.

[how]
Moved virtual_link_encoder and virtual_stream_encoder to dc/dio/virtual/.
Moved virtual_link_hwss to dc/link/hwss/ and renamed to link_hwss_virtual.
Removed dc/virtual/ directory.
Updated all includes and build files (Makefiles)

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Bhuvanachandra Pinninti <bpinnint@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>