This retrieves Xen's recommended address range for grant table and
interrupt for event channel. The interrupt is forwarded to the Xen
interrupt handling code.
Originally the device was "xen0", but "xen-dt0" should hopefully be
clearer in boot messages. The address range is for grant table and
the interrupt is used for the event channel.
This was originally implemented by Julien Grall in 2014. This is was
broken off of a much larger commit.
Submitted by: Elliott Mitchell <firstname.lastname@example.org>
Original implementation: Julien Grall <email@example.com>, 2014-01-13 17:40:58