sh: Conditionalize gUSA support.

This conditionalizes gUSA support. gUSA is not supported on
SMP configurations, and it's not necessary there anyways due
to having other atomicity options (ie, movli.l/movco.l).

Anything implementing the LL/SC semantics (all SH-4A CPUs)
can switch to userspace atomicity implementations without
requiring gUSA. This is left default-enabled on all UP so
that glibc doesn't break.

Those that know what they are doing can disable this explicitly.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/kernel/process.c b/arch/sh/kernel/process.c
index cd8dae1..b446999 100644
--- a/arch/sh/kernel/process.c
+++ b/arch/sh/kernel/process.c
@@ -350,7 +350,7 @@
 	unlazy_fpu(prev, task_pt_regs(prev));
 #endif
 
-#ifdef CONFIG_PREEMPT
+#if defined(CONFIG_GUSA) && defined(CONFIG_PREEMPT)
 	{
 		struct pt_regs *regs;