Make board attaching table driven and move it out into the soc

Make board attaching table driven and move it out into the soc
directories.  Move the device tables while here as was done in bitrig.
With these changes the only use of the board id defines is in the soc
directories.

Tested by matthieu and djm on imx and myself on omap and sunxi (qemu).
ok djm@, ok jasper@ on an earlier version