KVM: arm: Enable emulation of the physical timer

Set the handlers to emulate read and write operations for CNTP_CTL,
CNTP_CVAL and CNTP_TVAL registers in such a way that VMs can use the
physical timer.

Signed-off-by: Jérémy Fanguède <j.fanguede@virtualopensystems.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>