lp: move compat_ioctl handling into lp.c

Handling for LPSETTIMEOUT can easily be done in lp_ioctl, which
is the only user. As a positive side-effect, push the BKL
into the ioctl methods.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>