qemu-riscv: update to qemu-2.11.92pre60378_f733c7b5f

This obsoletes two of the included patches, one of them RISC-V specific,
since they've been picked up by upstream.

This build has been confirmed as being able to build and run an (extremely
recent) RISC-V Fedora 28 Rawhide image, available from:

    https://fedorapeople.org/groups/risc-v/disk-images/



Signed-off-by: Austin Seipp <aseipp@pobox.com>