markers: Add samples subdir

Begin infrastructure for kernel code samples in the samples/ directory.
Add its Kconfig and Kbuild files.
Source its Kconfig file in all arch/ Kconfigs.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Makefile

@@ -773,6 +773,9 @@ endef
 vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) $(kallsyms.o) vmlinux.o FORCE
 ifdef CONFIG_HEADERS_CHECK
 	$(Q)$(MAKE) -f $(srctree)/Makefile headers_check
+endif
+ifdef CONFIG_SAMPLES
+	$(Q)$(MAKE) $(build)=samples
 endif
 	$(call vmlinux-modpost)
 	$(call if_changed_rule,vmlinux__)

lib/Kconfig.debug

@@ -498,3 +498,5 @@ config FAULT_INJECTION_STACKTRACE_FILTER
 	select FRAME_POINTER
 	help
 	  Provide stacktrace filter for fault-injection capabilities
+
+source "samples/Kconfig"

samples/Kconfig

@@ -0,0 +1,11 @@
+# samples/Kconfig
+
+menuconfig SAMPLES
+	bool "Sample kernel code"
+	help
+	  You can build and test sample kernel code here.
+
+if SAMPLES
+
+
+endif # SAMPLES