Enable spidev drivers to support BLE modules on SANTVEND boards.

Depending on the revision of hardware, different drivers should be used:
- in case of v1.2 revision, it is equipped with ISP091201 BLE module
which is governed by special "spidevas" driver which implements its own
chip select handling.
- in case of v1.3 revision, it is equipped with Protues-III BLE module,
which is governed by standard "spidev" driver.

It was decided to build the "spidevas" driver as a kernel module.

Signed-off-by: Dmitry Petrov <dmitry.petrov@rtsoft.de>