vp8: [loongson] optimize regular quantize v2.
vp8: [loongson] optimize regular quantize v2.

1. Optimize the memset with mmi.
2. Optimize macro REGULAR_SELECT_EOB.

Change-Id: Icd9c866b0e6aef08874b2f123e9b0e09919445ff

webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx