iommu: Fix IOMMU debugfs fallout

A change made in the final version of IOMMU debugfs support replaced the
public function iommu_debugfs_new_driver_dir() by the public dentry
iommu_debugfs_dir in <linux/iommu.h>, but forgot to update both the
implementation in iommu-debugfs.c, and the patch description.

Fix this by exporting iommu_debugfs_dir, and removing the reference to
and implementation of iommu_debugfs_new_driver_dir().

Fixes: bad614b24293ae46 ("iommu: Enable debugfs exposure of IOMMU driver internals")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

iommu: Enable debugfs exposure of IOMMU driver internals

Provide base enablement for using debugfs to expose internal data of an
IOMMU driver. When called, create the /sys/kernel/debug/iommu directory.

Emit a strong warning at boot time to indicate that this feature is
enabled.

This function is called from iommu_init, and creates the initial DebugFS
directory. Drivers may then call iommu_debugfs_new_driver_dir() to
instantiate a device-specific directory to expose internal data.
It will return a pointer to the new dentry structure created in
/sys/kernel/debug/iommu, or NULL in the event of a failure.

Since the IOMMU driver can not be removed from the running system, there
is no need for an "off" function.

Signed-off-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>