qemu: Use '-machine hpet=off' instead of '-no-hpet'

qemu: Use '-machine hpet=off' instead of '-no-hpet'

qemu is about to deprecate the '-no-hpet' option in favor of configuring
the timer via '-machine'.

Use the QEMU_CAPS_MACHINE_HPET capability to switch to the new syntax
and mask out the old QEMU_CAPS_NO_HPET capability at the same time to
prevent using the old syntax.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>