ARM: highbank: select required errata work-arounds

Ensure necessary errata work-arounds are always enabled for Highbank
and Midway platforms. Highbank requires 764369 and 764369. Midway requires
798181, but only the first half of the work-around (no IPI). Support for
skipping the IPI is introduced in another commit.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>