printk: synchronize %p formatting documentation

printk: synchronize %p formatting documentation

Move all pointer-formatting documentation to one place in the code and one
place in the documentation instead of keeping it in three places with
different level of completeness.  Documentation/printk-formats.txt has
detailed information about each modifier, docstring above pointer() has
short descriptions of them (as that is the function dealing with %p) and
docstring above vsprintf() is removed as redundant.  Both docstrings in
the code that were modified are updated with a reminder of updating the
documentation upon any further change.

[[email protected]: fix comment]
Signed-off-by: Martin Kletzander <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>