SERIAL_BFIN=m or SERIAL_MUX=m shouldn't allow SERIAL_CORE_CONSOLE=y.

Additionally, this patch fixes whitespace instead of tabs at the
SERIAL_MUX_CONSOLE option.
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: Bryan Wu <bryan.wu@analog.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>