We're about to move the call to nodeDeviceSysfsGetSCSIHostCaps from
node_device_driver into virnodedeviceobj, so move the guts of the code
from the driver specific node_device_linux_sysfs into its own API
since virnodedeviceobj cannot callback into the driver.

Nothing in the code deals with sysfs anyway, as that's hidden by the
various virSCSIHost* and virVHBA* utility function calls.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>