x86: Document x86_init.paging.pagetable_init()

Signed-off-by: Attilio Rao <attilio.rao@citrix.com>
Acked-by:  <konrad.wilk@oracle.com>
Cc: <Ian.Campbell@citrix.com>
Cc: <Stefano.Stabellini@eu.citrix.com>
Cc: <xen-devel@lists.xensource.com>
Link: http://lkml.kernel.org/r/1345580561-8506-6-git-send-email-attilio.rao@citrix.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>