USB: usblp: add dynamic URBs, fix races

This patch's main bulk aims to make usblp the premier driver for code
pillaging once again. The code is as streamlined as possible and is bug-free
as possible. The usb-skeleton performs the same function, but is somewhat
abstract. The usblp is usb-skeleton which is actually used by many.

Since I combed a few small bugs away, this also fixes the small races we
had in usblp for a while. For example, now it's possible for several threads
to make write(2) calls (sounds silly, but consider a printer for paper
record, where every line of text is self-contained and thus it's all right
to have them interleaved). Also gone are issues with interrupts using
barriers dangerously.

This patch makes use of Oliver's anchor, and so it must trail the anchor
patch on the way to Linus.

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>