Adds new submodule for build automation

Introduces a submodule for build-related tasks, linking to the external repository for Xilinx ISE build scripts.

This facilitates streamlined build automation by integrating external tools.

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "libs/AXI-HS-Scheduler"]
 	path = libs/AXI-HS-Scheduler
 	url = ssh://git@git.0xmax42.io:33612/maxp/AXI-HS-Scheduler.git
+[submodule "build"]
+	path = build
+	url = git@github.com:0xMax42/Xilinx-ISE-Build.git