serial: samsung: Add poll_get_char & poll_put_char

The following patch allows users to use KGDB over serial console on
board based on Samsung SOC. It has been tested on a board using
exynos5.

[dianders: changed poll to return NO_POLL_CHAR, which appears to
fix 'help' in kgdb; also updated commit message]

Signed-off-by: Julien Pichon <pichon.jln@gmail.com>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>