We shouldn't really use the CONFIG_ARCH_U8500 option directly, but rather
have our own dedicated Kconfig option, so let's add that.

Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>