Refactor CONFIG_SPE check on Linux/powerpc

Commit 5401472 adds a check to call enable_kernel_spe and
disable_kernel_spe only if CONFIG_SPE is defined. Refactor this check
in a way similar to what CONFIG_ALTIVEC and CONFIG_VSX are checked, in
order to remove redundant kfpu_begin() and kfpu_end() implementations.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: WHR <msl0000023508@gmail.com>
Closes openzfs#14623

include/os/linux/kernel/linux/simd_powerpc.h

@@ -80,40 +80,32 @@
 #define	ENABLE_KERNEL_VSX
 #define	DISABLE_KERNEL_VSX
 #endif
-#ifdef CONFIG_SPE
-#define	kfpu_begin()				\
-	{					\
-		preempt_disable();		\
-		ENABLE_KERNEL_ALTIVEC		\
-		ENABLE_KERNEL_VSX		\
-		enable_kernel_spe();		\
-	}
-#define	kfpu_end()				\
-	{					\
-		disable_kernel_spe();		\
-		DISABLE_KERNEL_VSX		\
-		DISABLE_KERNEL_ALTIVEC		\
-		preempt_enable();		\
-	}
-#else /* CONFIG_SPE */
+#ifdef	CONFIG_SPE
+#define	ENABLE_KERNEL_SPE	enable_kernel_spe();
+#define	DISABLE_KERNEL_SPE	disable_kernel_spe();
+#else
+#define	ENABLE_KERNEL_SPE
+#define	DISABLE_KERNEL_SPE
+#endif
 #define	kfpu_begin()				\
 	{					\
 		preempt_disable();		\
 		ENABLE_KERNEL_ALTIVEC		\
 		ENABLE_KERNEL_VSX		\
+		ENABLE_KERNEL_SPE		\
 	}
 #define	kfpu_end()				\
 	{					\
+		DISABLE_KERNEL_SPE		\
 		DISABLE_KERNEL_VSX		\
 		DISABLE_KERNEL_ALTIVEC		\
 		preempt_enable();		\
 	}
-#endif
 #else
 /* seems that before 4.5 no-one bothered */
 #define	kfpu_begin()
 #define	kfpu_end()		preempt_enable()
-#endif
+#endif	/* Linux version >= 4.5 */
 
 #define	kfpu_init()		0
 #define	kfpu_fini()		((void) 0)