Implement arm64 insns:
ADDP s_2s, d_2d 
FADDP 2d_2d_2d, 4s_4s_4s, 2s_2s_2s 
FMAX d_d, s_s 
FMIN d_d, s_s 
FMAXNM d_d, s_s (not really correct) 
FMINNM d_d, s_s (not really correct) 
FCVT{A,N}S W,D 



git-svn-id: svn://svn.valgrind.org/vex@2993 8f6e269a-dfd6-0310-a8e1-e2731360e62c