Introduce a mechanism that performs an handshake between the userspace
provider and kernel driver which verifies that the user supports all
required features in order to operate correctly.

The handshake verifies the needed functionality by comparing the reported
device caps and the provider caps. If the device reports a non-zero
capability the appropriate comp mask is required from the userspace
provider in order to allocate the context.

Link: https://lore.kernel.org/r/20200722140312.3651-4-galpress@amazon.comReviewed-by: Shadi Ammouri <sammouri@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>