devices: virtio: video: split OutputResources out of Context
devices: virtio: video: split OutputResources out of Context

Some fields of the `Context` struct are related to the output
resources. These fields should be cleared together. This CL
consolidates these fields to another struct to make the code clear.

Note that we add `keep_resources` and `set_output_buffer_count` fields
into OutputResources struct. Originally these two fields are not
cleared with other fields together. So this CL is not just a refactor
CL, it changes the reset logic.

BUG=b:168557465
TEST=pass android.media.cts.AdaptivePlaybackTest#testVP8_adaptiveDrc

Change-Id: I6843e835b6c488e74623704618ee54a5273eb7ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2416067
Tested-by: Chih-Yu Huang <f815e8cb2f117b8947610323682cb280404b8de3@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>
Reviewed-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>
Commit-Queue: Chih-Yu Huang <f815e8cb2f117b8947610323682cb280404b8de3@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm