haven: watchdog: Add virtual watchdog support

This driver takes advantage of the watchdog api in
the hypervisor through the use of ARM SMCCC calls.
It allows for communication between the watchdog
code in the kernel, and the watchdog api in the
hypervisor.

Change-Id: I9406f066fb9fd1b808a4b52a328b0c6c8185238e
Signed-off-by: Branden Bonaby <bbonaby@codeaurora.org>