RDMA/erdma: Add cmdq implementation

Cmdq is the main control plane channel between erdma driver and hardware.
After erdma device is initialized, the cmdq channel will be active in the
whole lifecycle of this driver.

This commit also includes two modifications from Christophe, one is using
the bitmap API to allocate bitmaps instead of hand-writing, and another
is using the non-atomic bitmap API when applicable.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christophe JAILLET <[email protected]>
Signed-off-by: Cheng Xu <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: hz-cheng