In some rare randconfig builds, CRC16 is disabled, which leads
to a link error:

drivers/input/keyboard/applespi.o: In function `applespi_send_cmd_msg':
applespi.c:(.text+0x449f): undefined reference to `crc16'
drivers/input/keyboard/applespi.o: In function `applespi_verify_crc':
applespi.c:(.text+0x7538): undefined reference to `crc16'

This symbol is meant to be selected for each user in Kconfig,
so do that here as well.

Fixes: 038b1a05 ("Input: add Apple SPI keyboard and trackpad driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>