This was removed as part of some Diab cleanup, however it is needed
and without the definition we get the following when building
for the FRDM-K64F board:
arm-none-eabi-ld: warning: cannot find entry symbol __start; not setting start address
Change-Id: Ie0604a600b6f7a4faa321c58aa63c5617a163107
Signed-off-by: Anas Nashif <anas.nashif@intel.com>