ibft: separate ibft parsing from sysfs interface

Not all iscsi drivers support ibft. For drivers like be2iscsi
that do not but are bootable through a vendor firmware specific
format/process this patch moves the sysfs interface from the ibft code
to a lib module. This then allows userspace tools to search for iscsi boot
info in a common place and in a common format.

ibft iscsi boot info is exported in the same place as it was
before: /sys/firmware/ibft.

vendor/fw boot info gets export in /sys/firmware/iscsi_bootX, where X is the
scsi host number of the HBA. Underneath these parent dirs, the
target, ethernet, and initiator dirs are the same as they were before.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>
Signed-off-by: Peter Jones <pjones@redhat.com>