gpio: add support of new GPIO direction flag

This commit manages the new dir flags that can be used in gpio
specifiers to indicate the pull-up or pull-down resistor
configuration for output gpio (GPIO_PULL_UP, GPIO_PULL_DOWN)
or the Open Drain/Open Source configuration for input gpio
(GPIO_OPEN_DRAIN, GPIO_OPEN_SOURCE).

These flags are already supported in Linux kernel in gpio lib.

This patch only parse and save the direction flags in GPIO
descriptor (desc->flags), it prepares the introduction of new ops
to manage them.
The GPIO uclass supports new GPIO flags from device-tree
(GPIO_XXX define in include/dt-bindings/gpio/gpio.h)
and translate them in the dir flags (GPIOD_XXX):
- GPIO_PULL_UP     => GPIOD_PULL_UP
- GPIO_PULL_DOWN   => GPIOD_PULL_DOWN
- GPIO_OPEN_DRAIN  => GPIOD_OPEN_DRAIN
- GPIO_OPEN_SOURCE => GPIOD_OPEN_SOURCE

This patch also adds protection in the check_dir_flags function for
new invalid configuration of the dir flags.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/asm-generic/gpio.h

@@ -119,8 +119,12 @@ struct gpio_desc {
 	unsigned long flags;
 #define GPIOD_IS_OUT		BIT(1)	/* GPIO is an output */
 #define GPIOD_IS_IN		BIT(2)	/* GPIO is an input */
-#define GPIOD_ACTIVE_LOW	BIT(3)	/* value has active low */
+#define GPIOD_ACTIVE_LOW	BIT(3)	/* GPIO is active when value is low */
 #define GPIOD_IS_OUT_ACTIVE	BIT(4)	/* set output active */
+#define GPIOD_OPEN_DRAIN	BIT(5)	/* GPIO is open drain type */
+#define GPIOD_OPEN_SOURCE	BIT(6)	/* GPIO is open source type */
+#define GPIOD_PULL_UP		BIT(7)	/* GPIO has pull-up enabled */
+#define GPIOD_PULL_DOWN		BIT(8)	/* GPIO has pull-down enabled */
 
 	uint offset;		/* GPIO offset within the device */
 	/*