aspeed: Support AST2600A1 silicon revision

aspeed: Support AST2600A1 silicon revision

There are minimal differences from Qemu's point of view between the A0
and A1 silicon revisions.

As the A1 exercises different code paths in u-boot it is desirable to
emulate that instead.

Signed-off-by: Joel Stanley <[email protected]>
Reviewed-by: Andrew Jeffery <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Message-id: 20200504093703[email protected]
Signed-off-by: Peter Maydell <[email protected]>