dt-bindings: pinctrl: add a 'drive-strength-microamp' property

This property allow drive-strength parameter in uA instead of mA.
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

@@ -258,6 +258,7 @@ drive-push-pull		- drive actively high and low
 drive-open-drain	- drive with open drain
 drive-open-source	- drive with open source
 drive-strength		- sink or source at most X mA
+drive-strength-microamp	- sink or source at most X uA
 input-enable		- enable input on pin (no effect on output, such as
 			  enabling an input buffer)
 input-disable		- disable input on pin (no effect on output, such as
@@ -326,6 +327,8 @@ arguments are described below.
 
 - drive-strength takes as argument the target strength in mA.
 
+- drive-strength-microamp takes as argument the target strength in uA.
+
 - input-debounce takes the debounce time in usec as argument
   or 0 to disable debouncing