aspeed/smc: Drop AspeedSMCController structure

aspeed/smc: Drop AspeedSMCController structure

The characteristics of the Aspeed controllers are described in a
AspeedSMCController structure which is redundant with the
AspeedSMCClass. Move all attributes under the class and adapt the code
to use class attributes instead.

This is a large change but it is functionally equivalent.

Signed-off-by: Cédric Le Goater <clg@kaod.org>