dt-bindings: mtd: brcmnand: Add brcmnand, brcmnand-v7.3 support

Added brcm,brcmnand-v7.3 as possible compatible string to support
brcmnand controller v7.3.
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Documentation/devicetree/bindings/mtd/brcm,brcmnand.txt

@@ -28,6 +28,7 @@ Required properties:
                          brcm,brcmnand-v7.0
                          brcm,brcmnand-v7.1
                          brcm,brcmnand-v7.2
+                         brcm,brcmnand-v7.3
                          brcm,brcmnand
 - reg              : the register start and length for NAND register region.
                      (optional) Flash DMA register range (if present)