fw/layer1: Add common TPU win setup/cleanup code

fw/layer1: Add common TPU win setup/cleanup code

Instead of each primitive doing it independently, if there is a TPU
scenario in one of the item, we do a common setup with the base tn
returned by rfch_get_params.

Then each rx / tx window setup is relative to that 'base tn'. For
TX window, you have to explicitely request an offset of 3. (this
would allow for some test code to TX on ts=0 for eg.)

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>