bus: bt1-apb: Build the driver into the kernel

Seeing trigger_all_cpu_backtrace() isn't exported from the kernel and
since calling it is a very important part of driver, which may provide
a better description of a possible cause of the error, let's disable the
ability to build the driver as a loadable kernel module.

Link: https://lore.kernel.org/r/20200528193113.17372-1-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Olof Johansson <olof@lixom.net>
Cc: soc@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>