rc: fix bugs in using boundary condition for cu while encoding each frame.

fixes the binary mismatch in 2 pass completely.
copy_cnt_4 avx2 asm code: nit, same speedup by sse version
denoiseDct unit test code: fixed bound value problem
denoiseDct asm code: nit faulty code, need a new SSE version
denoiseDct: nit unused asm function declarations
rc: improvements for cbr