kvmtool: ARM: timers: add "always-on" property to the device tree

The new optional property "always-on" indicates that the timers
are, well, always on when used with KVM.

This allows for substantial performance improvement in the guest
(it switches to NOHZ instead of using a periodic tick per vcpu)
and removes a lot of burden from the host (no need to inject tons
of interrupts with the associated rescheduling overhead).

Old kernels that don't understand this property will simply ignore it.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
kvmtool: arm64: fix compilation error

Currently tools/kvm doesn't build on arm64 when gtk3 is present.  The error looks like this:

  LINK     lkvm
ui/gtk3.o: In function `kvm_gtk_key_press':
/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:201: undefined reference to `kbd_queue'
/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:204: undefined reference to `kbd_queue'
/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:216: undefined reference to `kbd_queue'
/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:217: undefined reference to `kbd_queue'
/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:218: undefined reference to `kbd_queue'
ui/gtk3.o:/extra/sb/linux-kvm/tools/kvm/ui/gtk3.c:219: more undefined references to `kbd_queue' follow
collect2: error: ld returned 1 exit status
make: *** [lkvm] Error 1

The patch below makes the error go away and the resulting lkvm runs on arm64.

Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Joel Schopp <joel.schopp@amd.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>