package/powerpc-utils: Add powerpc hardware utilities

This change adds a package definition for the powerpc-utils project,
containing a set of powerpc-specific hardware management utilities.

We're using a git tag from upstream, which contains a few build-system
fixes.

[Thomas:
 - Add dependency on PowerPC architecture in Config.in.
 - Add homepage in Config.in help text.]

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>