staging: ion: Set minimum carveout heap allocation order to PAGE_SHIFT

In carveout heap, change minimum allocation order from 12 to
PAGE_SHIFT. After this change each bit in bitmap (genalloc -
General purpose special memory pool) represents one page size
memory.

Cc: sprd-ind-kernel-group@googlegroups.com
Cc: sanjeev.yadav@spreadtrum.com
Cc: Colin Cross <ccross@android.com>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Rajmal Menariya <rajmal.menariya@spreadtrum.com>
[jstultz: Reworked commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>