ARM: 8078/1: get rid of hardcoded assumptions about kernel stack size

Changing kernel stack size on arm is not as simple as it should be:
1) THREAD_SIZE macro doesn't respect PAGE_SIZE and THREAD_SIZE_ORDER
2) stack size is hardcoded in get_thread_info macro

This patch fixes it by calculating THREAD_SIZE and thread_info address
taking into account PAGE_SIZE and THREAD_SIZE_ORDER.

Now changing stack size becomes simply changing THREAD_SIZE_ORDER.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>