Merge remote-tracking branch 'remotes/palmer/tags/riscv-for-master-5.0-sf5' into staging

RISC-V Patches for the 5.0 Soft Freeze, Part 5

This tag contains the last of the patches I'd like to target for the 5.0 soft
freeze.  At this point we're mostly collecting fixes, but there are a few new
features.  The changes include:

* An OpenSBI update, including the various bits necessary to put CI together
  and an image for the 32-bit sifive_u board.
* A fix that disallows TSR when outside of machine mode.
* A fix for VS-mode interrupt forwarding.

# gpg: Signature made Tue 17 Mar 2020 03:59:58 GMT
# gpg:                using RSA key 2B3C3747446843B24A943A7A2E1319F35FBB1889
# gpg:                issuer "palmer@dabbelt.com"
# gpg: Good signature from "Palmer Dabbelt <palmer@dabbelt.com>" [unknown]
# gpg:                 aka "Palmer Dabbelt <palmer@sifive.com>" [unknown]
# gpg:                 aka "Palmer Dabbelt <palmerdabbelt@google.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 00CE 76D1 8349 60DF CE88  6DF8 EF4C A150 2CCB AB41
#      Subkey fingerprint: 2B3C 3747 4468 43B2 4A94  3A7A 2E13 19F3 5FBB 1889

* remotes/palmer/tags/riscv-for-master-5.0-sf5:
  target/riscv: Fix VS mode interrupts forwarding.
  gitlab-ci.yml: Add jobs to build OpenSBI firmware binaries
  riscv: sifive_u: Update BIOS_FILENAME for 32-bit
  roms: opensbi: Add 32-bit firmware image for sifive_u machine
  roms: opensbi: Upgrade from v0.5 to v0.6
  target/riscv: Correctly implement TSR trap

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>