[PATCH] Ressurrect the esp serial driver

Another first pass rescue run.  Fix up for modern locking, make it build
and check over.  It could still do with other fixes (sleep_on etc) but it's
a start
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>