lightnvm: remove dependencies on BLK_DEV_NVME and PCI

No need to force NVMe device driver to be compiled in if the
lightnvm subsystem is selected. Also no need for PCI to be selected
as well, as it would be selected by the device driver that hooks into
the subsystem.

Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>