IB: Replace ib_umem page_size by page_shift

IB: Replace ib_umem page_size by page_shift

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 <[email protected]>
CC: Steve Wise <[email protected]>
CC: Lijun Ou <[email protected]>
CC: Shiraz Saleem <[email protected]>
CC: Adit Ranadive <[email protected]>
CC: Dennis Dalessandro <[email protected]>
CC: Ram Amrani <[email protected]>
Signed-off-by: Artemy Kovalyov <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Acked-by: Ram Amrani <[email protected]>
Acked-by: Shiraz Saleem <[email protected]>
Acked-by: Selvin Xavier <[email protected]>
Acked-by: Selvin Xavier <[email protected]>
Acked-by: Adit Ranadive <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>