compal-laptop: Make it depend on CONFIG_RFKILL

-tip testing found this build failure (x86 randconfig):

 drivers/built-in.o: In function `setup_rfkill':
 compal-laptop.c:(.text+0x36abe8): undefined reference to `rfkill_alloc'
 compal-laptop.c:(.text+0x36abfc): undefined reference to `rfkill_register'
 compal-laptop.c:(.text+0x36ac30): undefined reference to `rfkill_alloc'
 compal-laptop.c:(.text+0x36ac44): undefined reference to `rfkill_register'

Which can happen with CONFIG_COMPAL_LAPTOP=y but COMPAL_LAPTOP=m.

Signed-off-by: Ingo Molnar <mingo@elte.hu>