[POWERPC] Add cpu feature for SPE handling

Make it so that SPE support can be determined at runtime.  This is similiar
to how we handle AltiVec.  This allows us to have SPE support built in and
work on processors with and without SPE.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index e477c9d..57c589c 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -669,9 +669,13 @@
 	 * mode (asyn, precise, disabled) for 'Classic' FP. */
 	if (val & PR_FP_EXC_SW_ENABLE) {
 #ifdef CONFIG_SPE
-		tsk->thread.fpexc_mode = val &
-			(PR_FP_EXC_SW_ENABLE | PR_FP_ALL_EXCEPT);
-		return 0;
+		if (cpu_has_feature(CPU_FTR_SPE)) {
+			tsk->thread.fpexc_mode = val &
+				(PR_FP_EXC_SW_ENABLE | PR_FP_ALL_EXCEPT);
+			return 0;
+		} else {
+			return -EINVAL;
+		}
 #else
 		return -EINVAL;
 #endif
@@ -697,7 +701,10 @@
 
 	if (tsk->thread.fpexc_mode & PR_FP_EXC_SW_ENABLE)
 #ifdef CONFIG_SPE
-		val = tsk->thread.fpexc_mode;
+		if (cpu_has_feature(CPU_FTR_SPE))
+			val = tsk->thread.fpexc_mode;
+		else
+			return -EINVAL;
 #else
 		return -EINVAL;
 #endif