irqchip: GICv3: Check if GIC register access is controlled

Add support to configure ITS registers only if higher
exception levels have not already configured them.

Change-Id: I45eaa51e56e034d011cf41d8b924fb674f63447d
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>
[rishabhb: resolved merge conflict]
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>