Merge remote-tracking branch 'remotes/rth/tags/pull-axp-20190325' into staging

Update palcode for machine checks.

# gpg: Signature made Mon 25 Mar 2019 23:09:24 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/tags/pull-axp-20190325:
  pc-bios: Update palcode-clipper

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