powerpc/kvm: Fix build errors with older toolchains

On a box with gcc 4.3.2, I see errors like:

arch/powerpc/kvm/book3s_hv_rmhandlers.S:1254: Error: Unrecognized opcode: stxvd2x
arch/powerpc/kvm/book3s_hv_rmhandlers.S:1316: Error: Unrecognized opcode: lxvd2x
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -1251,7 +1251,7 @@ BEGIN_FTR_SECTION
 	reg = 0
 	.rept	32
 	li	r6,reg*16+VCPU_VSRS
-	stxvd2x	reg,r6,r3
+	STXVD2X(reg,r6,r3)
 	reg = reg + 1
 	.endr
 FTR_SECTION_ELSE
@@ -1313,7 +1313,7 @@ BEGIN_FTR_SECTION
 	reg = 0
 	.rept	32
 	li	r7,reg*16+VCPU_VSRS
-	lxvd2x	reg,r7,r4
+	LXVD2X(reg,r7,r4)
 	reg = reg + 1
 	.endr
 FTR_SECTION_ELSE