drivers:hv: Lock access to hyperv_mmio resource tree

drivers:hv: Lock access to hyperv_mmio resource tree

BugLink: http://bugs.launchpad.net/bugs/1616677
In existing code, this tree of resources is created
in single-threaded code and never modified after it is
created, and thus needs no locking.  This patch introduces
a semaphore for tree access, as other patches in this
series introduce run-time modifications of this resource
tree which can happen on multiple threads.

Signed-off-by: Jake Oshins <jakeo@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(back ported from commit e16dad6bfe1437aaee565f875a6713ca7ce81bdf)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
 Conflicts:
	drivers/hv/vmbus_drv.c
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>