drm/amd/display: Restore analog connector support

drm/amd/display: Restore analog connector support

[Why]
The analog connector support was accidentally removed,
causing a crash when connecting an analog monitor.

[How]
This patch restores the functions and pointers required for proper analog
and DP bridge encoder support on legacy GPUs.

V2: Restore the external encoder control functions.

V3:
 - Restore BIOS parser external encoder DAC load detection
 - Restore stream initialization and source selection changes

Fixes: e56e3cff2a1b ("drm/amd/display: Sync dcn42 with DC 3.2.373")
Cc: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>