libcamera: formats: add numPlanes helper

Determine the number of planes used by a format by counting the number
of PixelFormatPlaneInfo entries with a valid entry.

Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/formats.h

@@ -46,6 +46,8 @@ public:
 	unsigned int frameSize(const Size &size,
 			       const std::array<unsigned int, 3> &strides) const;
 
+	unsigned int numPlanes() const;
+
 	/* \todo Add support for non-contiguous memory planes */
 	const char *name;
 	PixelFormat format;