locking/static_keys: Provide DECLARE and well as DEFINE macros

We will need to provide declarations of static keys in header
files. Provide DECLARE_STATIC_KEY_{TRUE,FALSE} macros.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/816881cf85bd3cf13385d212882618f38a3b5d33.1472754711.git.tony.luck@intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>