powerpc/8xx: Save r3 all the time in DTLB miss handler

We are spending between 40 and 160 cycles with a mean of 65 cycles in
the DTLB handling routine (measured with mftbl) so make it more
simple althought it adds one instruction.
With this modification, we get three registers available at all time,
which will help with following patch.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: NScott Wood <oss@buserror.net>

arch/powerpc/kernel/head_8xx.S

@@ -385,23 +385,20 @@ InstructionTLBMiss:
 
 	. = 0x1200
 DataStoreTLBMiss:
-#ifdef CONFIG_8xx_CPU6
 	mtspr	SPRN_SPRG_SCRATCH2, r3
-#endif
 	EXCEPTION_PROLOG_0
-	mfcr	r10
+	mfcr	r3
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
 	 */
-	mfspr	r11, SPRN_MD_EPN
-	IS_KERNEL(r11, r11)
+	mfspr	r10, SPRN_MD_EPN
+	IS_KERNEL(r11, r10)
 	mfspr	r11, SPRN_M_TW	/* Get level 1 table */
 	BRANCH_UNLESS_KERNEL(3f)
 	lis	r11, (swapper_pg_dir-PAGE_OFFSET)@ha
 3:
-	mtcr	r10
-	mfspr	r10, SPRN_MD_EPN
+	mtcr	r3
 
 	/* Insert level 1 index */
 	rlwimi	r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
@@ -453,9 +450,7 @@ DataStoreTLBMiss:
 	MTSPR_CPU6(SPRN_MD_RPN, r10, r3)	/* Update TLB entry */
 
 	/* Restore registers */
-#ifdef CONFIG_8xx_CPU6
 	mfspr	r3, SPRN_SPRG_SCRATCH2
-#endif
 	mtspr	SPRN_DAR, r11	/* Tag DAR */
 	EXCEPTION_EPILOG_0
 	rfi