fs: run filesystem hooks under fakeroot

fs: run filesystem hooks under fakeroot

Currently, the pre-gen hooks of the various filesystems are run before
we enter the fakeroot.

However, this precludes those hooks from doing actions that require
root, like creating a pseudo-device or the likes.

So, move those pre-gen hooks under fakeroot.

This has currently no side-effect, as they are still called before
everything else in the fakeroot script, even the system-wide chown call.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>