Create a new include file for the pl022's device struct,
type macros, etc, so that it can be instantiated using
the "embedded struct" coding style.

While we're adding the new file to MAINTAINERS, add
also the .c file, which was missing an entry.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180820141116.9118-16-peter.maydell@linaro.org
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>