Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-nios-20220303' into staging

Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-nios-20220303' into staging

Rewrite nios2 interrupt handling

# gpg: Signature made Thu 03 Mar 2022 19:52:33 GMT
# gpg:                using RSA key 7A481E78868B4DB6A85A05C064DF38E8AF7E215F
# gpg:                issuer "richard.henderson@linaro.org"
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>" [full]
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth-gitlab/tags/pull-nios-20220303:
  target/nios2: Rewrite interrupt handling
  target/nios2: Special case ipending in rdctl and wrctl
  target/nios2: Split mmu_write
  target/nios2: Hoist R_ZERO check in rdctl
  target/nios2: Only build mmu.c for system mode
  target/nios2: Replace MMU_LOG with tracepoints
  target/nios2: Remove mmu_read_debug

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