Size of pages are held by struct ib_umem in page_size field.

It is better to store it as an exponent, because page size by nature
is always power-of-two and used as a factor, divisor or ilog2's argument.

The conversion of page_size to be page_shift allows to have portable
code and avoid following error while compiling on ARM:

  ERROR: "__aeabi_uldivmod" [drivers/infiniband/core/ib_core.ko] undefined!

CC: Selvin Xavier <selvin.xavier@broadcom.com>
CC: Steve Wise <swise@chelsio.com>
CC: Lijun Ou <oulijun@huawei.com>
CC: Shiraz Saleem <shiraz.saleem@intel.com>
CC: Adit Ranadive <aditr@vmware.com>
CC: Dennis Dalessandro <dennis.dalessandro@intel.com>
CC: Ram Amrani <Ram.Amrani@Cavium.com>
Signed-off-by: NArtemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: NLeon Romanovsky <leon@kernel.org>
Acked-by: NRam Amrani <Ram.Amrani@cavium.com>
Acked-by: NShiraz Saleem <shiraz.saleem@intel.com>
Acked-by: NSelvin Xavier <selvin.xavier@broadcom.com>
Acked-by: NSelvin Xavier <selvin.xavier@broadcom.com>
Acked-by: NAdit Ranadive <aditr@vmware.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>