ARM: samsung: move CONFIG_DEBUG_S3C_UART to Kconfig.debug

Before we can separate plat-samsung from the individual platforms,
this one has to get moved to a place where it remains accessible.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200806182059.2431-13-krzk@kernel.org


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>