RDMA/mlx5: align MR mem allocation size to power-of-two

RDMA/mlx5: align MR mem allocation size to power-of-two

The MR memory allocation requests extra bytes to guarantee that there
is enough space to find the memory aligned to MLX5_UMR_ALIGN.

For power-of-two sizes, the alignment can be guaranteed by kmalloc()
according to commit 59bb47985c1d ("mm, sl[aou]b: guarantee natural
alignment for kmalloc(power-of-two)").

So if target alignment is power-of-two and adding the extra bytes
crosses a power-of-two boundary, use the next power-of-two as the
allocation size.

Signed-off-by: Yuanyuan Zhong <yzhong@purestorage.com>
Link: https://lore.kernel.org/r/20230629213248.3184245-2-yzhong@purestorage.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>