init: Move stack canary initialization after setup_arch

Stack canary intialization involves getting a random number.
Getting this random number may involve accessing caches or other
architectural specific features which are not available until
after the architecture is setup. Move the stack canary initialization
later to accomodate this.

Change-Id: I00b564a2c3172229a44339c061fa380c17fe7d8e
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>