Save registers before handling interrupts.
Save registers before handling interrupts.

Somehow the hardware drivers we're too bothered about this omission,
but the virtio drivers seemed to crap out quickly.  IOW, virtio drivers
now work reliably.

ujamjar/rumpuser-baremetal,ujamjar/rumpuser-baremetal,rumpkernel-attic/rumprun-baremetal,rumpkernel-attic/rumprun-baremetal,rumpkernel-attic/rumprun-baremetal,ujamjar/rumpuser-baremetal