Documentation/printk-formats.txt: No casts needed for u64/s64

Now all 64-bit architectures have been converted to int-ll64.h in kernel
space, casting to (unsigned) long long is no longer needed when formatting
u64/s64.

For backwards compatibility, alpha, ia64, mips64, and powerpc64 still use
int-l64.h in userspace.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>