media/gpu/chromeos: Change IP storage type config

The ImageProcessor::PortConfig previously contained a vector of
VideoFrame::StorageType's. However, the vector was only ever configured
to be one long.

This changes the PortConfig storage_type vector to a singleton.

Doing this simplifies the ImageProcessorBackend Create() functions since
they no longer need to loop through the vector. Also the Create()
functions can pass the original input and output PortConfig arguments
to the constructor. Previously, a new PortConfig was created with the
first "acceptable" storage type.

Bug: None
Test: Chrome compiles.
Test: Decoding and encoding tests pass.
Test: image_processor_tests pass.
Change-Id: Ie80b206137187ab4ab5d201c4ec1ae1767c9a11c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5403671


Commit-Queue: Nathan Hebert <nhebert@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280244}