dt-bindings: pinctrl: meson: update register descriptions

like pull-enable, pull should be optional has this region is available on
every controllers. Also, the g12a feature a new region "ds" for the
drive-strength

All this region thing is one big mess. I suspect that there is only one
big GPIO region with holes in it. All registers between the current
regions reads '0' so it is probably just spare space to handle more pins.

Since we need to continue to handle the existing controllers, switching to
one single region now would not simplify things. However, if more
organisation layouts and features keep on being added, we may have to look
at this again

Fixes: 3cd3c83f67 ("pinctrl: Add compatibles for Amlogic Meson G12A pin controllers")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

@@ -23,11 +23,11 @@ The GPIO bank for the controller is represented as a sub-node and it acts as a
 GPIO controller.
 
 Required properties for sub-nodes are:
- - reg: should contain address and size for mux, pull-enable, pull and
-   gpio register sets
- - reg-names: an array of strings describing the "reg" entries. Must
-   contain "mux", "pull" and "gpio". "pull-enable" is optional and
-   when it is missing the "pull" registers are used instead
+ - reg: should contain a list of address and size, one tuple for each entry
+   in reg-names.
+ - reg-names: an array of strings describing the "reg" entries.
+   Must contain "mux" and "gpio".
+   May contain "pull", "pull-enable" and "ds" when appropriate.
  - gpio-controller: identifies the node as a gpio controller
  - #gpio-cells: must be 2