arch: x86: fix jailhouse build

The jailhouse board's build is currently broken.

It wants to depend on the qemu board's devicetree, but can no longer
do so since the board-level dts files were moved into individual board
directories.

To restore the build, insert the qemu_x86.dts contents into
x86_jailhouse.dts.

Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>