arm64: Add temporary ERRATA_MIDR_ALL_VERSIONS compatibility macro

MIDR_ALL_VERSIONS is changing, and won't have the same meaning
in 4.17, and the right thing to use will be ERRATA_MIDR_ALL_VERSIONS.

In order to cope with the merge window, let's add a compatibility
macro that will allow a relatively smooth transition, and that
can be removed post 4.17-rc1.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>