kernel: banner: cleanup `#ifdef`'s
kernel: banner: cleanup `#ifdef`'s

Cleanup the mess of duplicate function definitions, unnecessary
variables and duplicate strings. All banner strings are now constant in
ROM. Also fixes a double space between the end of the version string and
the trailing `***` when there is no boot delay.

Signed-off-by: Jordan Yates <d74a90e280bbad1cc3646781a4e234b467b60fe1@data61.csiro.au>

finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr