arm: mc: neon: Reduce usage of general purpose registers in blend/blend_v functions

	                	A73		A53
                	Current	Earlier	Current	Earlier
blend_h_w2_8bpc_neon:	74.1	74.1	137.5	137.5
blend_h_w4_8bpc_neon:	65.8	65.8	147.1	147.1
blend_h_w8_8bpc_neon:	68.9	68.7	131.7	131.7
blend_h_w16_8bpc_neon:	86	85.6	190.3	190.4
blend_h_w32_8bpc_neon:	149.2	149.8	358	358.3
blend_h_w64_8bpc_neon:	263.1	264.1	629.8	630.3
blend_h_w128_8bpc_neon:	571	575.4	1404.5	1404.2
blend_v_w2_8bpc_neon:	118.7	120.1	195.3	196.4
blend_v_w4_8bpc_neon:	245.8	247.2	357.3	358.4
blend_v_w8_8bpc_neon:	202	204.2	357.2	358.4
blend_v_w16_8bpc_neon:	234.8	238.5	591.3	591.8
blend_v_w32_8bpc_neon:	344.4	347.2	994.7	997.2
blend_w4_8bpc_neon:	37.5	38.3	96.7	98.7
blend_w8_8bpc_neon:	53	54.8	123.3	125.3
blend_w16_8bpc_neon:	151	150.8	332.4	334.5
blend_w32_8bpc_neon:	370.9	361.6	908.4	910.7