clockevents: Clean up clockchips.h

Do various cleanups on the clockchips.h file:

 - indent preprocessor blocks to make it more clear which block we are in,
   this also makes merge resolution easier

 - comment larger preprocessor blocks consistently, using the:

     #if FOO
     ...
     #else /* !FOO: */
     ...
     #endif /* !FOO */

   notation.

 - unbreak lines

 - etc.

No change in functionality.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>