Fix lost interrupts.
Update seabios-hppa.

# gpg: Signature made Sat 16 Mar 2019 16:13:42 GMT
# gpg:                using RSA key 64DF38E8AF7E215F
# 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/tags/pull-hppa-20190316:
  Update seabios-hppa to latest upstream
  target/hppa: Avoid squishing DISAS_IAQ_N_STALE_EXIT

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