[enh] use Misc() properties in trellis' PCF

[chmousset]

Currently Misc() properties are ignored when generating the pcf constraint file for trellis.

To keep compatibility with existing platforms, Lattice's Diamond properties are translated to nextpnr's.
Only PULLUP has been successfully tested (on icestick), but PULLUP_RESISTOR should be supported aswell, based on document found here (p91)

the IOStandard() properties are not supported by nextpnr, therefore nothing is done with them.

[sbourdeauducq]

Hmm, the idea behind Misc() is to allow toolchain-specific attributes that are just passed as-is.
How about adding Pullup() instead (and migrating existing code)?