csky: Add kmemleak support

Here is the log after enabled:

[    1.798972] kmemleak: Kernel memory leak detector initialized (mem pool available: 15851)
[    1.798983] kmemleak: Automatic memory scanning thread started
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/Kconfig

@@ -43,6 +43,7 @@ config CSKY
 	select HAVE_CONTEXT_TRACKING
 	select HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select HAVE_DEBUG_BUGVERBOSE
+	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_FUNCTION_TRACER