kernel: init: use C implementation for STACK_CANARY_INIT

Due to a limitation on XCC, the inline assembly does not
produce the expected instructions. This results in a wrong
code sequence. On the other hand, plain C code works well.
The note about compilers seems to not be an issue on any of
our currently supported compilers.

Change-Id: I9d2ab0fbf8a48d9dad51da3fd54453f205516d74
Signed-off-by: Mazen NEIFER <mazen@nestwave.com>
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>