[OE-core] Add recipe for hplip 3.12.6

[Marc Reilly]

Hi,

This adds a recipe for hplip 3.12.6 with a configuration targeted for USB 
printers. I'm not much of a linux printing expert, so just went with a
setup that let me print all the different doc types required.

This is based on a recipe for an earlier version which didn't seem to make it
into oe-core. I'm guessing that oe-core is the correct place for it: next to
cups, ghostscript and foomatic.

Cheers,
Marc