aspeed/sli: Add AST2700 support

AST2700 SLI engine is designed to accelerate the
throughput between cross-die connections.
It have CPU_SLI at CPU die and IO_SLI at IO die.

Introduce dummy AST2700 SLI and SLIIO models.

Signed-off-by: Troy Lee <troy_lee@aspeedtech.com>
Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
4 files changed