ArmPkg/ArmLib: move set/way helper functions into private header

ArmPkg/ArmLib: move set/way helper functions into private header

The clean/invalidate helper functions that operate on a single cache
line identified by set, way and level in a special, architected format
are only used by the implementations of the clean/invalidate routines
that operate on the entire cache hierarchy, as exposed by ArmLib.

The latter routines will be deprecated soon, so move the helpers out
of ArmLib.h and into a private header so they are safe from abuse.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>