multi-kernel: Allow inclusion in regular kernel build flow, deploy improvements

multi-kernel: Allow inclusion in regular kernel build flow, deploy improvements

  * user proper name for *Image in deploy
   * Moved from do_compile to seperate task, pre-configure step
   * Context save/restore the regular defconfig, so we don't break the normal flow
   * Install binaries and .configs + create symlinks
   * Add deploy_append step to install normal flow .config in same fashion
   * When there are no additional configs defined the do_compileconfigs() method changes to a NOOP

Signed-off-by: Roger Monk <r-monk@ti.com>
Signed-off-by: Koen Kooi <k-kooi@ti.com>