whpx: arm64: clamp down IPA size Code taken from HVF and adapted for WHPX use. Note that WHPX doesn't have a default vs maximum IPA distinction. Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr> Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>