drivers: bcm2835_isp: Allow multiple users for the ISP driver.

Add a second (identical) set of device nodes to allow concurrent use of the ISP
hardware by another user. This change effectively creates a second state
structure (struct bcm2835_isp_dev) to maintain independent state for the second
user. Node and media entity names are appened with the instance index
appropriately.

Further users can be added by changing the BCM2835_ISP_NUM_INSTANCES define.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>