media/gpu/v4l2: Support mainline Linux device paths

Upstream Linux does not use the ChromeOS-specific device path patterns
for "-dec", "-enc" etc. Add support for the respective mainline patterns
in order to improve HW de-/encoding support.

This crucially requires us to enumerate a lot of /dev/video* devices, as
it has become common for SoCs to have >100 of them - usually most of
them used for ISPs. Unfortunately enumerating many devices - even
non-existing ones, as we don't know ahead of time in sandboxed
environments - is not free. Using 256 takes roughly 30-60ms on platforms
like RK3399 or MT8390 respectively, while raising the number to e.g.
1024 would take it to >100ms, and was therefor used as solid limit.

Given that the increased time cost only applies to non-ChromeOS Linux
with `use_v4l2_codec` enabled, the tradeoff is likely justified, as
chances are high that affected platforms do support HW-decoding in a lot
of cases and profit a lot from using it.

The change here is enough to make HW video decoding work on various
stacks, with both stateful and stateless V4L2.

Note that similar places used in tests or with the experimental
`V4L2FlatStatefulVideoDecoder` feature where left out for now.

Bug: b:334110478
Change-Id: I9ea18aef05502c7796a61dcf15b13edc27845cd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5872600
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Ted (Chromium) Meyer <tmathmeyer@chromium.org>
Reviewed-by: Nathan Hebert <nhebert@chromium.org>
Commit-Queue: Nathan Hebert <nhebert@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1368857}