Now that we have Timers probed from DT, don't need legacy domain

This however requires mapping to be called explicitly for the IRQ which
still can't (and probably never) be probed from DT such as IPI and
SOFTIRQ
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>