target-arm: Provide mechanism for getting KVM constants even if not CONFIG_KVM

There are a number of places where it would be convenient for ARM
code to have working definitions of KVM constants even in code
which is compiled with CONFIG_KVM not set. In this situation we
can't simply include the kernel KVM headers (which might conflict
with host header definitions or not even compile on the compiler
we're using) so we have to redefine equivalent constants.
Provide a mechanism for doing this and checking that the values
match, and use it for the constants we're currently exposing
via an ad-hoc mechanism.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Message-id: 1385140638-10444-2-git-send-email-peter.maydell@linaro.org
