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

Alas the method trigger_all_cpu_backtrace() isn't exported by the
kernel, but we need to have it called in case of the bus errors detected
to get a better description of a possible cause of the error. Let's
disable the ability to build the driver as a loadable kernel module then.
Note In future the driver will support the AXI-bus interconnect capability,
so we'd have to make it built into the kernel anyway.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Serge Semin <[e-mail]>
Cc: Alexey Malahov <[e-mail]>
Cc: Olof Johansson <[e-mail]>
Cc: [e-mail]
Signed-off-by: Arnd Bergmann <[e-mail]>

drivers/bus/Kconfig

···
 	  accessed via corresponding sysfs nodes.
 
 config BT1_AXI
-	tristate "Baikal-T1 AXI-bus driver"
+	bool "Baikal-T1 AXI-bus driver"
 	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
 	select MFD_SYSCON
 	help