KVM: arm64: Enable the EL1 physical timer for AArch32 guests

Some 32bits guest OS can use the CNTP timer, however KVM does not
handle the accesses, injecting a fault instead.

Use the proper handlers to emulate the EL1 Physical Timer (CNTP)
register accesses of AArch32 guests.

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