aspeed/smc: Use the RAM memory region for DMAs

Instead of passing the memory address space region, simply use the RAM
memory region instead. This simplifies RAM accesses.

This patch breaks migration compatibility.

Fixes: c4e1f0b4 ("aspeed/smc: Add support for DMAs")
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20210407171637.777743-2-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>