arm: Remove support for unused s3c64xx

Following the removal of the smdk6400 board, the s3c64xx SoC becomes unused, so
remove associated code. It will still be possible to restore it later from the
Git history if necessary.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>

include/common.h

@@ -647,7 +647,6 @@ ulong	get_PCI_freq (void);
 #endif
 #if defined(CONFIG_S3C24X0) || \
     defined(CONFIG_LH7A40X) || \
-    defined(CONFIG_S3C6400) || \
     defined(CONFIG_EP93XX)
 ulong	get_FCLK (void);
 ulong	get_HCLK (void);