hdl/modules/position_calc/dds_lut: add DDS LUT

This is a first step to use a custom DDS
specific to our application
models/*: add Sysgen custom DDS blackbox
models/ddc_bpm_476_066.mdl: update model

 - Replace the Xilinx DDS by a custom one.
 In effect, it's just simple LUT outputting
 cos and -sin, for now.

 - Remove input DDC BPF. It is not really necessary
 and it constraints the DDC IF to the BPF passband
hdl/modules/position_calc/generated/virtex6/*: update generated files

Replace the Xilinx power-2 DDS by a
custom DDS specific to our application
hdl/modules/position_calc/generated/artix7/*: update generated files

Replace the Xilinx power-2 DDS by a
custom DDS specific to our application
Merge branch 'pos_calc_wishbonized' into devel