classmate-laptop: depends on RFKILL or RFKILL=n

Randy Dunlap has reported that building classmate-laptop fails when
CONFIG_RFKILL=m and CONFIG_ACPI_CMPC=y. He suggested depending on
RFKILL, but, then, it will not be possible to select classmate-laptop
when RFKILL is off. There's no known problem with building and using
classmate-laptop with RFKILL off. So depend on RFKILL or RFKILL=n.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: platform-driver-x86@vger.kernel.org
Cc: Daniel Oliveira Nascimento <don@syst.com.br>