[POWERPC] 4xx: Add mfspr/mtspr inline macros to 4xx bootwrapper

The 4xx bootwrapper occasionally needs to access SPR registers,
this adds mfspr/mtspr wrappers to it.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Josh Boyer <[e-mail]>

arch/powerpc/boot/reg.h

···
 	return pvr;
 }
 
+#define __stringify_1(x)	#x
+#define __stringify(x)		__stringify_1(x)
+
+#define mfspr(rn)	({unsigned long rval; \
+			asm volatile("mfspr %0," __stringify(rn) \
+				: "=r" (rval)); rval; })
+#define mtspr(rn, v)	asm volatile("mtspr " __stringify(rn) ",%0" : : "r" (v))
+
 register void *__stack_pointer asm("r1");
 #define get_sp()	(__stack_pointer)