serial: samsung: remove all uses of get_clksrc and set_clksrc

With clkdev based clock lookup support, the clock set and get operation
using clock names communicated between the samsung uart driver and the
SoC specific extension can be removed.

In addition to that, for each platform specific extension, add the
default clock selection, number of clock options for uart baud generator,
clock selection bit mask and shift values which is required by the
clkdev support in samsung uart driver.

The default clock selection value 'def_clk_sel' specifies the default clock
to be used as the source clock for baud rate generator in case the platform
code does not specify the same.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>