x64Emitter: add BLEND* instructions
Jit64: use BLENDVPD in ps_sel

As magumagu noted, BLENDVPD actually _is_ useful for ps_sel (but only in
combination with CMPPD).
x64Emitter: add different bitnesses of CVT*2SI
Jit64: implement fctiw/fctiwz
x64Emitter: add CVTTPD2DQ
Jit64: use CVTPD2DQ/CVTTPD2DQ in ps_sel

As suggested by magumagu. In the case that b is not bound to a register
yet, this saves a MOVD.