docs:aspeed: Add AST2700 Evaluation board

Add AST2700 Evaluation board and its boot command.

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>
1 file changed