ad9434_fmc: Fix GPIO width

GPIO port width is 15 instead of 32
zed: Remove top level constraints

Remove top level constraints from the ZED base design.
ad9434_fmc: Remove top level constraints

Remove all the unnecessary top level constraint definitions.
fmcomms2_zc706: Remove top level constraints

Remove all the unnecessary top level constraint definitions.
ad9467_fmc: Made some cosmetic changes on the block design script.