ACPI, APEI, GHES, Prevent GHES to be built as module

GHES (Generic Hardware Error Source) is used to process hardware error
notification in firmware first mode.  But because firmware first mode
can be turned on but can not be turned off, it is unreasonable to
unload the GHES module with firmware first mode turned on.  To avoid
confusion, this patch makes GHES can be enabled/disabled in
configuration time, but not built as module and unloaded at run time.
Signed-off-by: NHuang Ying <ying.huang@intel.com>
Reviewed-by: NAndi Kleen <ak@linux.intel.com>
Reviewed-by: NMatthew Garrett <mjg@redhat.com>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/acpi/apei/Kconfig

@@ -10,7 +10,7 @@ config ACPI_APEI
 	  error injection.
 
 config ACPI_APEI_GHES
-	tristate "APEI Generic Hardware Error Source"
+	bool "APEI Generic Hardware Error Source"
 	depends on ACPI_APEI && X86
 	select ACPI_HED
 	help