sh64: Ensure KALLSYMS is enabled for unwinder use.

Since sh64 depends on kallsyms unconditionally for its stack unwinding to
be of any use, make sure it's selected. In practice we don't have any
case where it's disabled anyways, so moving to this to a select is fine.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig

@@ -55,6 +55,7 @@ config SUPERH32
 
 config SUPERH64
 	def_bool ARCH = "sh64"
+	select KALLSYMS
 
 config ARCH_DEFCONFIG
 	string