[why]
In current code, we recognize a pipe as a phantom pipe if it references
the same phantom stream. However it can also a phantom split pipe.
If the phantom split pipe has a smaller pipe index than the phantom pipe
we will mistakenly use the phantom split pipe as the phantom pipe. This
causes an incorrect subvp configuration where the first half of the
screen is flashing solid white image.

[how]
Add additional check that the pipe needs to be an 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>