serial: sh-sci: kgdb console build fixes.

The kgdb console code requires uart_set_options() and friends, which
are only provided by the serial core when console support is enabled.
These were sitting under CONFIG_SH_KGDB and resulted in a link error
when console support wasn't enabled, work that by rolling the console
routines under CONFIG_SH_KGDB_CONSOLE, which they should have been
all along.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>