pktcdvd: improve BKL and compat_ioctl.c usage

The pktcdvd driver uses proper locking and does not need the BKL in the
ioctl and llseek functions of the character device, so kill both.

Moving the compat_ioctl handling from common code into the driver itself
fixes build problems when CONFIG_BLOCK is disabled.

Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>