MAINTAINERS: Move Kukjin Kim to credits

MAINTAINERS: Move Kukjin Kim to credits

Kukjin Kim has been maintaining the Samsung ARM architectures since 2010
up to 2016.  He contributed many patches for the S3C, S5P and Exynos
support.  However since 2016 there is little activity from him on the
LKML [1] so move his name to the CREDITS.

Dear Kukjin, thank you for all the effort you put in to the upstream
Samsung support.

[1] https://lore.kernel.org/lkml/?q=f%3A%22Kukjin+Kim%22

Link: https://lore.kernel.org/r/20201016061848.6258-1-krzk@kernel.org
Cc: Kukjin Kim <kgene@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Olof Johansson <olof@lixom.net>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Kukjin Kim <kgene@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>