The implementation of cpu_mmu_index was split between cpu-common.h
and cpu-all.h, depending on CONFIG_USER_ONLY. We already have the
plumbing common to user and system mode. Using MMU_USER_IDX
requires the cpu.h for a specific target, and so is restricted to
when we're compiling per-target.
Include the new header only where needed.
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>