serial: push default_serial_console to drivers

serial: push default_serial_console to drivers

Rather than sticking arch/board/driver specific logic in the common
serial code, push it all out to the respective drivers.  The serial
drivers declare these funcs weak so that boards can still override
things with their own definition.

Signed-off-by: Mike Frysinger <[email protected]>
CC: Heiko Schocher <[email protected]>
CC: Anatolij Gustschin <[email protected]>
CC: Tom Rix <[email protected]>
CC: Minkyu Kang <[email protected]>
CC: Craig Nauman <[email protected]>
CC: Prafulla Wadaskar <[email protected]>
CC: Mahavir Jain <[email protected]>
Tested-by: Minkyu Kang <[email protected]>