Add serial console input handler

Serial console handler when registered allows to interact with serial
line. It can either execute callback from ISR or defer execution to
fiber or task. This will be used in Bluetooth development for tests and
simple interaction with Bluetooth stack.

Change-Id: Ia960b456a75062d614baea324608058d979aa11b
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
7 files changed