hplip: Introduce version 3.12.6

This introduces a recipe to build hplip 3.12.6 in a simple configuration
aimed at USB printers. It is based on a 3.11.3a recipe for oe classic
by Steve Sakoman.

The hp-setup program is patched to add a small delay after restarting cups,
as on slower embedded systems the cups daemon would sometimes not restart
quickly enough and adding a new printer would sporadically fail.

Tested on an armv6 system (with cups 1.4.6, ghostscript 9.05, foomatic).

Signed-off-by: Marc Reilly <marc@cpdesign.com.au>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>