[ARM] S3C2410: Add sysfs attribute for serial driver clock source

Add attribute to show the current clock source for the serial
driver and remove old and annoying debug output.

Note, this only currently shows the current source with a
"* " prefix to indicate that it is the current source. Future
code will list all the clock sources, with the non-selected
one with "  " prefix.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
PATCH FOLLOWS
KernelVersion: 2.6.26-rc3