imsm: add generic method to resolve "device" links

imsm: add generic method to resolve "device" links

Each virtual device is linked with parent by "device". This patch adds
possibility to get previous device in sysfs tree.

Depending on device type, there is a different amount of virutal
layers. The best we can do is allow to directly specify how many
"device" links need to be resolved. This approach also allows to get
previous virtual device, which may contain some attributes.

Simplify fd2devname, this function doesn't require new functionality and
shall use generic fd2kname.

For nvme drives represented via nvme-subystem when path to block
device if requested, then return it without translation.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>