tracing/stack-tracer: introduce CONFIG_USER_STACKTRACE_SUPPORT

Impact: cleanup

User stack tracing is just implemented for x86, but it is not x86 specific.

Introduce a generic config flag, that is currently enabled only for x86.
When other arches implement it, they will have to
SELECT USER_STACKTRACE_SUPPORT.

Signed-off-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7a146ba..e49a4fd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -36,6 +36,7 @@
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_GENERIC_DMA_COHERENT if X86_32
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
+	select USER_STACKTRACE_SUPPORT
 
 config ARCH_DEFCONFIG
 	string