Optimize x86 intra_predict_4x4 and 8x8

Optimize x86 intra_predict_4x4 and 8x8

High bit depth Penryn, Sandybridge cycles:
4x4_ddl: 11->10,  9-> 8
4x4_ddr: 15->13, 12->11
4x4_hd:        , 15->12
4x4_hu:        , 14->13
4x4_vr:  15->14, 14->12
8x8_ddl: 32->19, 19->14
8x8_ddr: 42->19, 21->14
8x8_hd:        , 15->13
8x8_hu:  21->17, 16->12
8x8_vr:  33->19,

8-bit Penryn, Sandybridge cycles:
4x4_ddr: 24->15,
4x4_hd:  24->16,
4x4_hu:  23->15,
4x4_vr:  23->16,
4x4_vl:  10-> 9,
8x8_ddl: 23->15,
8x8_hd:        , 17->14
8x8_hu:        , 15->14
8x8_vr:  20->16, 17->13