[why]
 when ODM + MPO is used for all 4 available pipes. Pipe transition will
 be nonseamless. Phantom OTG master pipe reuses the secondary OPP head
 pipe. There is no possible seamless path to transit to the new
 state. The correct logic would be to reuse a secondary DPP pipe as the
 phantom OTG master pipe. This way we are able to first transit the
 minimal transtion state of new and then transit to new state seamlessly.

 current                      New (nonseamless)
 ________________________     ________________________
 | plane0  slice0  stream0|   | plane0  slice0  stream0|
 |DPP0----OPP0----OTG0----|   |DPP0----OPP0----OTG0----|
 | plane1 |       |       |   | plane0  slice1 |       |
 |DPP2----|       |       |   |DPP2----OPP2----|       |
 | plane0  slice1 |       |   | plane0  slice0  stream1|
 |DPP1----OPP1----|       |   |DPP1----OPP1----OTG1----|
 | plane1 |               |   | plane0  slice1 |       |
 |DPP3----|               |   |DPP3----OPP3----|       |
 |________________________|   |________________________|

 New (seamless)               New (minimal transition)
 ________________________     ________________________
 | plane0  slice0  stream0|   | plane0  slice0  stream0|
 |DPP0----OPP0----OTG0----|   |DPP0----OPP0----OTG0----|
 | plane0  slice1 |       |   | plane0  slice1 |       |
 |DPP1----OPP1----|       |   |DPP1----OPP1----|       |
 | plane0  slice0  stream1|   |________________________|
 |DPP2----OPP2----OTG2----|
 | plane0  slice1 |       |
 |DPP3----OPP3----|       |
 |________________________|

[how]
Try to acquire free pipes used as secondary DPP pipes from current state
before try to acquire any free pipes for new OTG master pipe.
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@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>