media: ipu-bridge: Fix Kconfig dependencies

The current Kconfig symbol dependencies allow having the following Kconfig
symbol values

	CONFIG_IPU_BRIDGE=m
	CONFIG_VIDEO_IPU3_CIO2=y
	CONFIG_CIO2_BRIDGE=n

This does not work as the IPU bridge API is conditional to
IS_ENABLED(CONFIG_IPU_BRIDGE). Fix this by changing the dependencies so
that CONFIG_IPU_BRIDGE can be separately selected.

The CONFIG_CIO2_BRIDGE symbol becomes redundant as a result and is
removed.

Fixes: 2545a2c0 ("media: ipu3-cio2: allow ipu_bridge to be a module again")
Suggested-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>