drm/amd/display: Fix seamless boot sequence

[WHY]
When the system powers up eDP with external monitors in seamless boot
sequence, stutter get enabled before TTU and HUBP registers being
programmed, which resulting in underflow.

[HOW]
Enable TTU in hubp_init.
Change the sequence that do not perpare_bandwidth and optimize_bandwidth
while having seamless boot streams.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Lo-an Chen <lo-an.chen@amd.com>
Signed-off-by: Paul Hsieh <paul.hsieh@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>