ARM: dts: omap4-panda-common: Enable powering off the device

As the TWL6030 chip is the main power controller here, declare
it as system-power-controller

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Message-ID: <20240217082007.3238948-5-andreas@kemnade.info>
Signed-off-by: Tony Lindgren <tony@atomide.com>