fs: ext4: Switch to dentry cache implementation ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ext4: use kernel names for byte swaps ...

This is an adoption of the U-Boot commit

| commit 7f101be
| Author: Michael Walle <michael@walle.cc>
| Date:   Mon Aug 29 10:46:44 2016 +0200
|
|     ext4: use kernel names for byte swaps
|
|     Instead of __{be,le}{16,32}_to_cpu use {be,le}{16,32}_to_cpu.
|
|     Signed-off-by: Michael Walle <michael@walle.cc>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

fs: rename inode member of struct filep to priv ...

Because that's what it is. 'inode' will become confusing
once we support real inodes.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

fs: cleanup backingstore handling ...

All filesystem drivers which need a backingstore device do the same
ignoring of '/dev/' in the backingstore followed by a cdev_open. Add a
helper function for it and let the core handle the cdev. As a side
effect this makes sure that fsdev->cdev is also set when a device is
mounted without the leading '/dev/' which was previously ignored
by the mount code.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

fs: implement initial ext4 support from U-Boot ...

The ext4 implementation has been taken from U-Boot with some
changes:

- No global variables to allow for multiple filesystems to
  be mounted and multiple files to be open.
- remove fs internal link following and use the barebox link
  implementation.
- remove write support. This is incomplete in U-Boot, so I decided
  to skip this for now.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>