Missing axi_err_slv_intf and axi_lite_err_slv/axi_lite_err_slv_intf

Hello,

I'm using the `axi_lite_demux` module, and I would like to redirect the addresses that are not mapped to a module that returns with an error.

I see that right now this only exists for AXI full, and even in that case it doesn't use the AXI_BUS interface.

Can I create a pull request to add the missing modules, or do you have any specific reason to not include them?