dt-bindings: rng: add MediaTek MT7622 Hardware Random Generator bindings

Document the bindings used by MediaTek MT7622 SoC hardware random number
generator.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/mtk-rng.txt

@@ -2,7 +2,9 @@ Device-Tree bindings for Mediatek random number generator
 found in Mediatek SoC family
 
 Required properties:
-- compatible	    : Should be "mediatek,mt7623-rng"
+- compatible	    : Should be
+			"mediatek,mt7622-rng", 	"mediatek,mt7623-rng" : for MT7622
+			"mediatek,mt7623-rng" : for MT7623
 - clocks	    : list of clock specifiers, corresponding to
 		      entries in clock-names property;
 - clock-names	    : Should contain "rng" entries;