x86: Update x86-pinctrl driver device-tree-bindings doc

This updates the device-tree-bindings doc for x86-pinctrl driver:

 - clarify "gpio-offset" is required only when "mode-gpio" is set
 - correct property name "pull-strength"
 - use tab instead of space at several places

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/gpio/intel,x86-pinctrl.txt

@@ -9,7 +9,7 @@ The PINCTRL master node requires the following properties:
 Pin nodes must be children of the pinctrl master node and can
 contain the following properties:
 - pad-offset	- (required) offset in the IOBASE for the pin to configure
-- gpio-offset	- (required) 2 cells
+- gpio-offset	- (required only when 'mode-gpio' is set) 2 cells
 			- offset in the GPIOBASE for the pin to configure
 			- the bit shift in this register (4 = bit 4)
 - mode-gpio	- (optional) standalone property to force the pin into GPIO mode
@@ -18,16 +18,16 @@ contain the following properties:
 in case of 'mode-gpio' property set:
 - output-value	- (optional) this set the default output value of the GPIO
 - direction	- (optional) this set the direction of the gpio
-- pull-str	- (optional) this set the pull strength of the pin
+- pull-strength	- (optional) this set the pull strength of the pin
 - pull-assign	- (optional) this set the pull assignement (up/down) of the pin
-- invert            - (optional) this input pin is inverted
+- invert	- (optional) this input pin is inverted
 
 Example:
 
 pin_usb_host_en0@0 {
-    gpio-offset = <0x80 8>;
-    pad-offset = <0x260>;
-    mode-gpio;
-    output-value = <1>;
-    direction = <PIN_OUTPUT>;
+	gpio-offset = <0x80 8>;
+	pad-offset = <0x260>;
+	mode-gpio;
+	output-value = <1>;
+	direction = <PIN_OUTPUT>;
 };