vp8[loongarch]: Optimize vp8 encoding partial function

1. vp8_short_fdct4x4
2. vp8_regular_quantize_b
3. vp8_block_error
4. vp8_mbblock_error
5. vpx_subtract_block

Bug: webm:1755

Change-Id: I3dbfc7e3937af74090fc53fb4c9664e6cdda29ef
11 files changed