RDMA/siw: Use ib_umem_get() to pin user pages

Abandon siw private code to pin user pages during user
memory registration, but use ib_umem_get() instead.
This will help maintaining the driver in case of changes
to the memory subsystem.

Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
Link: https://lore.kernel.org/r/20231104075643.195186-1-bmt@zurich.ibm.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>