MAINTAINERS: aspeed: Add more files and myself as a reviewer

Add the rest of the ASPEED drivers that are in tree. Most are obvious,
except for ftgmac100 which matches the register layout used in the
ASPEED SoC.

I am the Linux maintainer for the ASPEED kernel port, and help maintain
the fork of u-boot used for OpenBMC, so add myself as a reviewer so I
can stay informed about u-boot changes.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>