kernfs: s/sysfs_dirent/kernfs_node/ and rename its friends accordingly

kernfs has just been separated out from sysfs and we're already in
full conflict mode.  Nothing can make the situation any worse.  Let's
take the chance to name things properly.

This patch performs the following renames.

* s/sysfs_elem_dir/kernfs_elem_dir/
* s/sysfs_elem_symlink/kernfs_elem_symlink/
* s/sysfs_elem_attr/kernfs_elem_file/
* s/sysfs_dirent/kernfs_node/
* s/sd/kn/ in kernfs proper
* s/parent_sd/parent/
* s/target_sd/target/
* s/dir_sd/parent/
* s/to_sysfs_dirent()/rb_to_kn()/
* misc renames of local vars when they conflict with the above

Because md, mic and gpio dig into sysfs details, this patch ends up
modifying them.  All are sysfs_dirent renames and trivial.  While we
can avoid these by introducing a dummy wrapping struct sysfs_dirent
around kernfs_node, given the limited usage outside kernfs and sysfs
proper, I don't think such workaround is called for.

This patch is strictly rename only and doesn't introduce any
functional difference.

- mic / gpio renames were missing.  Spotted by kbuild test robot.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Neil Brown <neilb@suse.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib.c

@@ -393,7 +393,7 @@ static const DEVICE_ATTR(value, 0644,
 
 static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
 {
-	struct sysfs_dirent	*value_sd = priv;
+	struct kernfs_node	*value_sd = priv;
 
 	sysfs_notify_dirent(value_sd);
 	return IRQ_HANDLED;
@@ -402,7 +402,7 @@ static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
 static int gpio_setup_irq(struct gpio_desc *desc, struct device *dev,
 		unsigned long gpio_flags)
 {
-	struct sysfs_dirent	*value_sd;
+	struct kernfs_node	*value_sd;
 	unsigned long		irq_flags;
 	int			ret, irq, id;