MFC 275207:

We don't use the hypervisor interrupt, make it optional in the device tree.

Submitted by: Julien Grall <julien.grall AT linaro.org>

MFC 275208:

Some device tree configurations place the generic timer under the root
of the tree and not under simplebus. Update the driver to handle this.

Submitted by: Julien Grall <julien.grall AT linaro.org>