dt-bindings: mfd: aspeed: Add AST2700 SCU compatibles

Add SCU interrupt controller compatible strings for the AST2700 SoC:
scu-ic0 to 3. This extends the MFD binding to support AST2700-based
platforms.

Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/all/20250908011812.1033858-3-ryan_chen@aspeedtech.com