powerpc/32: add helper to write into segment registers

This patch add an helper which wraps 'mtsrin' instruction
to write into segment registers.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/reg.h

@@ -1425,6 +1425,11 @@ static inline void msr_check_and_clear(unsigned long bits)
 #define mfsrin(v)	({unsigned int rval; \
 			asm volatile("mfsrin %0,%1" : "=r" (rval) : "r" (v)); \
 					rval;})
+
+static inline void mtsrin(u32 val, u32 idx)
+{
+	asm volatile("mtsrin %0, %1" : : "r" (val), "r" (idx));
+}
 #endif
 
 #define proc_trap()	asm volatile("trap")