soc: a64fx-diag: disable modular build

The NMI infrastructure cannot currently be used in loadable modules:

ERROR: modpost: "free_nmi" [drivers/soc/fujitsu/a64fx-diag.ko] undefined!
ERROR: modpost: "request_nmi" [drivers/soc/fujitsu/a64fx-diag.ko] undefined!
ERROR: modpost: "enable_nmi" [drivers/soc/fujitsu/a64fx-diag.ko] undefined!

Disable this for now to make allmodconfig build again. We may revisit
this and export those symbols instead in the future.

Reported-by: Sudip Mukherjee <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

drivers/soc/fujitsu/Kconfig

···
 menu "fujitsu SoC drivers"
 
 config A64FX_DIAG
-	tristate "A64FX diag driver"
+	bool "A64FX diag driver"
 	depends on ARM64
 	depends on ACPI
 	help