ARM: S5P64X0: no more support S5P6440 and S5P6450 SoCs

This patch removes supporting codes for s5p6440 and s5p6450 because
seems no more used now. And if its supporting is required, DT based
codes should be supprted next time.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>