ARM: dts: am335x: Guardian: Disable poweroff support from RTC

 * Disabling poweroff support form RTC will allow poweroff
   to handle from other machanism

Signed-off-by: Gireesh Hiremath <Gireesh.Hiremath@in.bosch.com>
Message-Id: <20220325100613.1494-5-Gireesh.Hiremath@in.bosch.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>