adi_board.tcl: add some optional parameters to ad_xcvrcon and ad_cpu_interconnect to support hierarchal designs

[aholtzma-am]

ad_xcvrcon

The port_prefix parameter allows an optional prefix to be applied to
port names created by ad_xcvrcon. This is useful when created large
hierarchical designs where all ports are prefixed by their hierarchical
name to avoid name clashes at the top level (for example: slot_a,
slot_b, slot_c, etc).

The resetn parameter sets the net name to be connected to ext_reset_in
on the reset generator. This parameter defaults to 'sys_cpu_resetn'.

ad_cpu_interconnect

Add an optional prefix, segment_prefix, to be applied to the segment to avoid name clashes. This is used when creating a block design in the root, and then moved to a hierarchical cell using move_bd_cells. Without the prefix, a second instance of this block design will have segment name conflicts because it uses the instance name before moving.