arm: kgdb: Handle read-only text / modules

Handle the case where someone has set the text segment of the kernel
as read-only by using the newly introduced "patch" mechanism.

Change-Id: Icb0494d7ec18d3dbfb547b55d17d5c274acf27e7
Signed-off-by: Doug Anderson <dianders@chromium.org>
[kees: switched structure size check to BUILD_BUG_ON (sboyd)]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Git-commit: 23a4e4050ba9c98ab67db0980a9fb20e5096d9ea
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>