libcamera: Add support for monochrome sensors

This commit adds support for monochrome (greyscale) raw sensors. These
are sensors that have no colour filter array, so all pixels are the
same and there are no distinct colour channels.

These sensors still require many of an ISP's processing stages, such
as denoise, tone mapping, but not those that involve colours (such as
demosaic, or colour matrices).

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/bayer_format.h

@@ -23,7 +23,8 @@ public:
 		BGGR = 0,
 		GBRG = 1,
 		GRBG = 2,
-		RGGB = 3
+		RGGB = 3,
+		MONO = 4
 	};
 
 	enum Packing : uint16_t {