Kbuild: Handle PREEMPT_RT for version string and magic

Kbuild: Handle PREEMPT_RT for version string and magic

Update the build scripts and the version magic to reflect when
CONFIG_PREEMPT_RT is enabled in the same way as CONFIG_PREEMPT is treated.

The resulting version strings:

  Linux m 5.3.0-rc1+ #100 SMP Fri Jul 26 ...
  Linux m 5.3.0-rc1+ #101 SMP PREEMPT Fri Jul 26 ...
  Linux m 5.3.0-rc1+ #102 SMP PREEMPT_RT Fri Jul 26 ...

The module vermagic:

  5.3.0-rc1+ SMP mod_unload modversions
  5.3.0-rc1+ SMP preempt mod_unload modversions
  5.3.0-rc1+ SMP preempt_rt mod_unload modversions

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>