atomisp: hmm: allow sleep when alloc_private_pages() is trying order == 0

atomisp: hmm: allow sleep when alloc_private_pages() is trying order == 0

BZ: 27472

For performance purpose, alloc_private_pages() tries to allocate pages
without allowing to sleep. But such approach may fail when system isn't
yet running out of memory.
This patch allows alloc_pages() to sleep when page order == 0, which
happens after a bigger order failed in atomic mode or even in case it was
the original requested order.

Change-Id: I9f1c83eac3aae973b4c7a2961a1b9c7dec3e72a6
Signed-off-by: David Cohen <david.a.cohen@intel.com>
Signed-off-by: Tuukka Toivonen <tuukka.toivonen@intel.com>
Tested-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Reviewed-on: http://android.intel.com:8080/40704
Reviewed-by: Koskinen, Ilkka <ilkka.koskinen@intel.com>
Reviewed-by: Kruger, Jozef <jozef.kruger@intel.com>
Tested-by: Lampila, KalleX <kallex.lampila@intel.com>
Reviewed-by: Wang, Wen W <wen.w.wang@intel.com>
Reviewed-by: Laakso, Antti <antti.laakso@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>