ARM: S3C2440: Fix plat-s3c24xx move of s3c2440/s3c2442 support

Commit 58bac7b8 failed to move the two
PLL files s3c2440-pll-12000000.c and s3c2440-pll-16934400.c, so place
these in arch/arm/mach-s3c2440 to fix this commit up.

As a note, these are not built by the default configuration and thus the
failure to move wasn't spotted until much later.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>