media: aspeed: Allow to capture from SoC display (GFX)

media: aspeed: Allow to capture from SoC display (GFX)

ASPEED BMC IC has 2 different display engines. Please find AST2600's
datasheet to get detailed information.

1. VGA on PCIe
2. SoC Display (GFX)

By default, video engine (VE) will capture video from VGA. This patch
adds an option to capture video from GFX with standard ioctl,
vidioc_s_input.

An enum, aspeed_video_input, is added for this purpose.
enum aspeed_video_input {
	VIDEO_INPUT_VGA = 0,
	VIDEO_INPUT_GFX,
	VIDEO_INPUT_MAX
};

To test this feature, you will need to enable GFX first. Please refer to
ASPEED's SDK_User_Guide, 6.3.x Soc Display driver, for more information.
In your application, you will need to use v4l2 ioctl, VIDIOC_S_INPUT, as
below to select before start streaming.

int rc;
struct v4l2_input input;

input.index = VIDEO_INPUT_GFX;
rc = ioctl(fd, VIDIOC_S_INPUT, &input);
if (rc < 0)
{
	...
}

Link: https://github.com/AspeedTech-BMC/openbmc/releases
Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
[hverkuil: split up three overly long lines]