hw/char: Introduce SH_SCI Kconfig entry

We want to be able to use the 'SH4' config for architecture
specific features. Add more fine-grained selection by adding
a CONFIG_SH_SCI selector for the SH4 serial controller.

Add the missing MAINTAINERS entries.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210222141514.2646278-5-f4bug@amsat.org>