ISE: Fix project paths

The ISE project cannot open as the HDL files have moved since it was
last used. Fix the paths so that it works again.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Add UART to design

This uses the Exar XR21V141x UART to USB bridge that is present on the
Digilent Atlys development board.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Add debug module

The debug module collects counters from the system for debugging.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Connect counters to system

This connects the debug counters to the appropriate points in the
system.

Signed-off-by: Joel Stanley <joel@jms.id.au>