dt: Add a camera regulator node to all downstream Pi platforms

The current firmware fixup of camera sensor overlays is not
particularly nice, and it stops you being able to load them
dynamically.
It's also incompatible with creating a simple DT that can be
loaded for both CAM1 and CAM0 on a CM as they would both
try to claim the one GPIO.

Almost all sensors have a hook of some form for a regulator, so
it's relatively straightforward to convert them all to use a
fixed regulator with GPIO control.

Add a fixed regulator node for each platform with the GPIO
correctly configured for the camera shutdown line. (The LED line
is ignored).

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>