kernel.h: move READ/WRITE definitions to <linux/types.h>

kernel.h: move READ/WRITE definitions to <linux/types.h>

Patch series "kernel.h: Move out a couple of macros and constants".

kernel.h hosts a couple of macros and constants that may be better placed.
Do that.  Also add missing documentation.  No functional changes
intended.

This patch (of 2):

Headers shouldn't be forced to include <linux/kernel.h> just to
gain these simple constants.

Link: https://lkml.kernel.org/r/20250324105228.775784-1-andriy.shevchenko@linux.intel.com
Link: https://lkml.kernel.org/r/20250324105228.775784-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexandru Ardelean <aardelean@baylibre.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>