termios: uninline conversion helpers

default go into drivers/tty/tty_ioctl.c, unusual - into
arch/*/kernel/termios.c (only alpha and sparc have those).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/YxDmeUBHo0s/Ew8b@ZenIV


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>