Move the s3c6400-clock.c implementation over to use the new common
plat-samsung based clock-clksrc.c.

Note, this does not delete the clocks definitions that are now unused
in the regs-clock.h to reduce the quantity of change in this commit.

Based on original patches by Harald Welte.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>