selftests: ncdevmem: Separate out dmabuf provider

[ Upstream commit 8b9049af ]

So we can plug the other ones in the future if needed.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20241107181211.3934153-3-sdf@fomichev.me


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 97c4e094 ("tests/ncdevmem: Fix double-free of queue array")
Signed-off-by: Sasha Levin <sashal@kernel.org>