ARM: pxa: ezx: fix a910 camera data

The camera_supply_dummy_device definition is shared between a780 and a910,
but only provided when the first is enabled and fails to build for a
configuration with only a910:

arch/arm/mach-pxa/ezx.c:1097:3: error: 'camera_supply_dummy_device' undeclared here (not in a function)

This moves the definition into its own section.

Fixes: 6c1b417a ("ARM: pxa: ezx: use the new pxa_camera platform_data")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>