documentation: Extend pinctrl docs for Meson8b

Add the compatible string for Meson8b in Meson pinctrl documentation
and add new information for Meson8b in source code comments.
Signed-off-by: Carlo Caione <carlo@endlessm.com>
Acked-by: Beniamino Galvani <b.galvani@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/meson,pinctrl.txt

 == Amlogic Meson pinmux controller ==
 
 Required properties for the root node:
- - compatible: "amlogic,meson8-pinctrl"
+ - compatible: "amlogic,meson8-pinctrl" or "amlogic,meson8b-pinctrl"
  - reg: address and size of registers controlling irq functionality
 
 === GPIO sub-nodes ===

drivers/pinctrl/meson/pinctrl-meson.c

@@ -13,8 +13,9 @@
 
 /*
  * The available pins are organized in banks (A,B,C,D,E,X,Y,Z,AO,
- * BOOT,CARD for meson6 and X,Y,DV,H,Z,AO,BOOT,CARD for meson8) and
- * each bank has a variable number of pins.
+ * BOOT,CARD for meson6, X,Y,DV,H,Z,AO,BOOT,CARD for meson8 and
+ * X,Y,DV,H,AO,BOOT,CARD,DIF for meson8b) and each bank has a
+ * variable number of pins.
  *
  * The AO bank is special because it belongs to the Always-On power
  * domain which can't be powered off; the bank also uses a set of