Reland (2): Linux Video Capture: Add support for multiplanar YUV420 format enumeration

Reland (2): Linux Video Capture: Add support for multiplanar YUV420 format enumeration

This is a relanding of the original CL mentioned below, with
a fix for bug http://crbug.com/448599, where some strange cameras
were listed.

The problem was the filtering out of devices with
V4L2_CAP_VIDEO_OUTPUT_MPLANE capabilities, which is the case for
the strange camera enumerated in the mentioned bug, corresponding
to a V4L2 memory-to-memory  graphics processor.

FI: the enumerated device is called exynos-gsc.m2m and is indeed
defined as having such capability in line [1]

[1] http://lxr.free-electrons.com/source/drivers/media/platform/exynos-gsc/gsc-m2m.c#L286

Original Reland description follows -------------------------------------
Relanding: Linux Video Capture: Add support for multiplanar YUV420 format enumeration.

This is a relanding of the original CL _with the designated initializers
changed by typical struct fields accesors_.

Note: Gcc does not support designated initializers and it seems that
there are still a few such builds around, hence the change.

Original CL description follows -----------------------------------------

multiplanar --> V4L2_CAP_VIDEO_CAPTURE_MPLANE

M420 is an example of I420 triplanar format, used
for testing and to be landed since there must be
at least one multiplanar format for this CL to be
consistent.

Following reviewer's hints, the VCDFLinux code is
refactored internally. Given that, some struct
initializations change from

struct A a = {}    _or_   struct A a; memset(&a, 0, sizeof(a));
a.bla1 = foo1;
a.bla2 = foo2;

to

struct A a = {
  .bla1 = foo1,
  .bla2 = foo2,
};

Which is a very common idiom to initialize structs in
interactions with V4L2 IOCTL. I'm introducing it here and
I'm planning to use it further in VCDLinux CLs down the line.

This CL only adds support for enumerating multiplane
format, while the actual capture will be reviewed in
a later CL (WIP @ http://crrev.com/804473008).

BUG=441836, 448599
Committed: https://crrev.com/c767957b50a6c04b7b804f310d76c0a59af44ced
Cr-Commit-Position: refs/heads/master@{#313525}

[mcasas, 2015-01-28 02:47:49]

mcasas@chromium.org changed reviewers:
+ posciak@chromium.org

[mcasas, 2015-01-28 02:47:50]

posciak@ PTAL

(Note the bugfix is made explicit between patches 0 and 1).

[Pawel Osciak, 2015-01-28 12:07:12]

lgtm

[mcasas, 2015-01-28 15:09:50]

The CQ bit was checked by mcasas@chromium.org

[commit-bot: I haz the power, 2015-01-28 15:10:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/877193005/20001

[commit-bot: I haz the power, 2015-01-28 16:41:35]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-28 16:42:52]

Patchset 2 (id:??) landed as
https://crrev.com/c767957b50a6c04b7b804f310d76c0a59af44ced
Cr-Commit-Position: refs/heads/master@{#313525}