MAINTAINERS: arm: samsung: include S3C headers in platform entry

Several S3C24xx/S3C64xx headers in include/linux are not caught by
Samsung S3C/S5P/Exynos maintainer entry and might look like abandoned.
Include them in "ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES"
entry.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20210210172303.335268-1-krzk@kernel.org

'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>