mm: add arch-independent testcases for RODATA

This patch makes arch-independent testcases for RODATA.  Both x86 and
x86_64 already have testcases for RODATA, But they are arch-specific
because using inline assembly directly.

And cacheflush.h is not a suitable location for rodata-test related
things.  Since they were in cacheflush.h, If someone change the state of
CONFIG_DEBUG_RODATA_TEST, It cause overhead of kernel build.

To solve the above issues, write arch-independent testcases and move it
to shared location.

[jinb.park7@gmail.com: fix config dependency]
  Link: http://lkml.kernel.org/r/20170209131625.GA16954@pjb1027-Latitude-E5410
Link: http://lkml.kernel.org/r/20170129105436.GA9303@pjb1027-Latitude-E5410
Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index afcc550..79d0fd1 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -90,3 +90,9 @@
 	  careful when enabling this feature because it adds about 30 KB to the
 	  kernel code.  However the runtime performance overhead is virtually
 	  nil until the tracepoints are actually enabled.
+
+config DEBUG_RODATA_TEST
+    bool "Testcase for the marking rodata read-only"
+    depends on STRICT_KERNEL_RWX
+    ---help---
+      This option enables a testcase for the setting rodata read-only.