MAINTAINERS: add entry for Aspeed I2C driver

Added myself as maintainer of the Aspeed I2C driver and the associated
I2C interrupt controller and added Joel Stanley and Benjamin
Herrenschmidt as reviewers.

Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>