From: Russell King <rmk+lkml@arm.linux.org.uk>

Russell was unable to correctly migrate this driver to the new
modem-control-signal API because

 TIOCMBIS/TIOCMBIC do not control only the DTR signal, but also the RTS,
 OUT1 and OUT2 signals, or even maybe nothing at all.  Plus, these IOCTLs
 are no longer passed down to the driver.  Instead, drivers should
 implement tiocmget and tiocmset driver methods.

so mark it as broken so as to not break allmodconfig/allyesconfig.