As per an unpublished document, in later reversion of chips
CP0St_{KX, SX, UX} is not writeable and hardcoded to 1.

Without those bits set, kernel is unable to access XKPHYS address
segment. So just set them up on CPU reset.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221031132531.18122-2-jiaxun.yang@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>