arm64: defconfig: Enable PDC irqchip, cmd_db and rpmh drivers

This change enables PDC irqchip, cmd_db and rpmh drivers as module.

Change-Id: I57ff2ca5e468ff4243bb8ce3a065a228e7bf9008
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
Signed-off-by: Veera Vegivada <vvegivad@codeaurora.org>