drivers: Import a very basic NVME implementation from Linux ...

Import a very abridged NVME implementation from Linux kernel in order
to be able to access NVME storage attached via PCIe.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>