arm64: dts: ti: k3-am65-main: Add system controller compatible

arm64: dts: ti: k3-am65-main: Add system controller compatible

Now that the TI K3 AM654 system controller bindings also cover the
usage in the main domain, add its compatible to address dtbs_check
complains:

  k3-am654-base-board.dtb: scm-conf@100000: compatible: ['syscon', 'simple-mfd'] is too short

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20250421214620.3770172-3-afd@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>