printk/cache: mark printk_once test variable __read_mostly

Add #include <linux/cache.h> to define __read_mostly.

Convert cache.h to use uapi/linux/kernel.h instead
of linux/kernel.h to avoid recursive #includes.

Convert the ALIGN macro to __ALIGN_KERNEL.

printk_once only sets the bool variable tested
once so mark it __read_mostly.

Neaten the alignment so it matches the rest of the
pr_<level>_once #defines too.

Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>