dt-bindings: gpio: stmpe: Remove node name requirement

STMPE driver does not require a specific node name anymore, only the
compatible is checked, update binding according to this.
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Documentation/devicetree/bindings/gpio/gpio-stmpe.txt

@@ -8,8 +8,7 @@ Optional properties:
  - st,norequest-mask: bitmask specifying which GPIOs should _not_ be requestable
    due to different usage (e.g. touch, keypad)
 
-Node name must be stmpe_gpio and should be child node of stmpe node to which it
-belongs.
+Node should be child node of stmpe node to which it belongs.
 
 Example:
 	stmpe_gpio {