serial: samsung: merge all SoC specific port reset functions

The port reset function in each of the platform specific extension performs
the same operations and hence all the reset port functions can be merged into
one and moved into the common samsung uart driver. The SoC specific port reset
functions are removed from SoC extensions.

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>