drm/amd/display: Handle seamless boot stream

A seamless boot stream has hardware resources assigned to it, and adding
a new stream means rebuilding the current assignment. It is desirable to
avoid this situation since it may cause light-up issues on the VGA
monitor on USB-C. This commit swaps the seamless boot stream to pipe 0
(if necessary) to ensure that the pipe context matches.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Co-developed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>