Move qemu to chipyard from firesim

.gitmodules

@@ -92,3 +92,6 @@
 [submodule "vlsi/hammer-mentor-plugins"]
 	path = vlsi/hammer-mentor-plugins
 	url = git@github.com:ucb-bar/hammer-mentor-plugins.git
+[submodule "toolchains/qemu"]
+	path = toolchains/qemu
+	url = https://github.com/qemu/qemu.git

scripts/build-toolchains.sh

@@ -121,6 +121,9 @@ cp -p "${SRCDIR}/riscv-isa-sim/build/libfesvr.a" "${RISCV}/lib/"
 CC= CXX= module_all riscv-pk --prefix="${RISCV}" --host=riscv64-unknown-elf
 module_all riscv-tests --prefix="${RISCV}/riscv64-unknown-elf"
 
+# Common tools (not in any particular toolchain dir)
+SRCDIR="$RDIR/toolchains" module_all qemu --prefix="${RISCV}" --target-list=riscv64-softmmu
+
 cd "$RDIR"
 
 {

scripts/init-submodules-no-riscv-tools.sh

@@ -30,6 +30,8 @@ cd "$RDIR"
 for name in toolchains/*/*/ ; do
     git config submodule."${name%/}".update none
 done
+git config submodule.toolchains.qemu.update none
+
 # Disable updates to the FireSim submodule until explicitly requested
 git config submodule.sims/firesim.update none
 # Disable updates to the hammer tool plugins repos