powerpc/spinlocks: Include correct header for static key

Recently, the spinlock implementation grew a static key optimization,
but the jump_label.h header include was left out, leading to build
errors:

  linux/arch/powerpc/include/asm/spinlock.h:44:7: error: implicit declaration of function ‘static_branch_unlikely’
   44 |  if (!static_branch_unlikely(&shared_processor))

This commit adds the missing header.

mpe: The build break is only seen with CONFIG_JUMP_LABEL=n.

Fixes: 656c21d6 ("powerpc/shared: Use static key to detect shared processor")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191223133147.129983-1-Jason@zx2c4.com

arch/powerpc/include/asm/spinlock.h

@@ -15,6 +15,7 @@
  *
  * (the type definitions are in asm/spinlock_types.h)
  */
+#include <linux/jump_label.h>
 #include <linux/irqflags.h>
 #ifdef CONFIG_PPC64
 #include <asm/paca.h>