RDMA/rxe: Cleanup page variables in rxe_mr.c

RDMA/rxe: Cleanup page variables in rxe_mr.c

BugLink: https://bugs.launchpad.net/bugs/2011425
[ Upstream commit 325a7eb85199ec9c5b5a7af812f43ea16b735569 ]

Cleanup usage of mr->page_shift and mr->page_mask and introduce
an extractor for mr->ibmr.page_size. Normal usage in the kernel
has page_mask masking out offset in page rather than masking out
the page number. The rxe driver had reversed that which was confusing.
Implicitly there can be a per mr page_size which was not uniformly
supported.

Link: https://lore.kernel.org/r/20230119235936.19728-6-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Stable-dep-of: 5ff31dfcd6d2 ("Subject: RDMA/rxe: Handle zero length rdma")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>