RDMA/erdma: Add the erdma module

Add the main erdma module, which provides interface to infiniband
subsystem.

This commit includes a modification from Christophe, that using the bitmap
API to allocate bitmaps instead of hand-writing. And the commit also fixes
warnings reported by static checkers.

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

Author: hz-cheng