Add ARC QEMU submodule

Add ARC QEMU as a submodule 'qemu_arc' in preparation for adding multiplatform host tool builds. Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio

.gitmodules

@@ -34,3 +34,6 @@
 [submodule "qemu"]
 path = qemu
 url = https://github.com/zephyrproject-rtos/qemu.git
+[submodule "qemu_arc"]
+path = qemu_arc
+url = https://github.com/foss-for-synopsys-dwc-arc-processors/qemu.git