kconfig: use zephyr as the binary name globally

do not use microkernel or nanokernel as the output binaries,
instead, use zephyr globally.

Also change the documentation to reflect this.

Change-Id: I8405761d1a0392c90cdfeec5c67d72eb4e5a76ff
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
21 files changed