Sort kernel device tree overlays alphabetically.

Signed-off-by: Vivien Didelot <[email protected]>

Add the device tree overlays for the supported cameras as listed on
https://www.raspberrypi.com/documentation/computers/camera_software.html#if-you-do-need-to-alter-the-configuration

Signed-off-by: Vivien Didelot <[email protected]>

The rpi-config package uses a mixture of sed -i $CONFIG and echo >>
$CONFIG commands in order to customize the config.txt file.

Because relying on commented out option is error prone, replace all
sed -i occurrences with the echo alternative.

Signed-off-by: Vivien Didelot <[email protected]>

Relying on a commented out config file fetched from a user Github
repository is likely error prone and misleading. The best practice
is to direct the user to the official documentation describing the
complete list of supported configuration keys.

Only a few keys are added to the config.txt file anyway, so start
from an empty file that the user may override if necessary.

Move the config.txt tweak code into do_compile for clarity and to
ensure that the 80 character wide check is done once the file is
modified, not in between appended modifications.

Signed-off-by: Vivien Didelot <[email protected]>

Instead of using many inconsistent variable flags like
VIDEO_CAMERA, RASPBERRYPI_CAMERA_V2, RASPBERRYPI_CAMERA_V3 or
RASPBERRYPI_HD_CAMERA, use a single RASPBERRYPI_CAMERA variable,
defaulting to "auto" for automatic camera detection, which can
be set to a specific camera module name or alias as described in
https://www.raspberrypi.com/documentation/computers/camera_software.html#if-you-do-need-to-alter-the-configuration

For convenience, provide variables for predefined values describing the
officially supported camera devices listed in the above documentation.

Signed-off-by: Vivien Didelot <[email protected]>

Reword the camera module section to describe the usage of the new
RASPBERRYPI_CAMERA variable.

Signed-off-by: Vivien Didelot <[email protected]>