ARM: make it easier to check the CPU part number correctly

Ensure that platform maintainers check the CPU part number in the right
manner: the CPU part number is meaningless without also checking the
CPU implement(e|o)r (choose your preferred spelling!)  Provide an
interface which returns both the implementer and part number together,
and update the definitions to include the implementer.

Mark the old function as being deprecated... indeed, using the old
function with the definitions will now always evaluate as false, so
people must update their un-merged code to the new function.  While
this could be avoided by adding new definitions, we'd also have to
create new names for them which would be awkward.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>