build a kernel, using malta_kvm_defconfig

(there's a lot in this config that I don't think is needed)

run-qemu.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash -p qemu
+
+qemu-system-mips -M malta -m 256 \
+ -append "earlyprintk=serial,ttyS0 console=ttyS0,38400n8 panic=10 oops=panic init=/bin/init loglevel=8 root=/dev/vda" \
+ -kernel $1  -nographic -display none -serial mon:stdio