Uvm reg block override using factory override

[AGS91]

Within build() function of top reg block you would instantiate these 3 sub-blocks and call configure , build , add_submap for them.
Then in your env ( or any tb component ) you simply need to instantiate the top_reg_block and call it’s build function

@mbc_dv

IP level, we need to use only 1 block from 3 available reg blocks without using compile defines ifdef.

Each IP could access the respective register block via top_reg_block_h.ip1_reg_block / top_reg_block_h.ip2_reg_block / top_reg_block_h.ip3_reg_block