linux-user: Pass CPUState to MAX_RESERVED_VA

Turn the scalar macro into a functional macro.  Move the creation
of the cpu up a bit within main() so that we can pass it to the
invocation of MAX_RESERVED_VA.  Delay the validation of the -R
parameter until MAX_RESERVED_VA is computed.

So far no changes to any of the MAX_RESERVED_VA macros to actually
use the cpu in any way, but ARM will need it.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20190822185929.16891-2-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>