math.h: amend abs() kernel-doc and add a note about signed type limits

math.h: amend abs() kernel-doc and add a note about signed type limits

- amend the kernel-doc so the description is decoupled from the
  parameter descriptions.

- add a note to explain behaviour for the signed types when supplied
  value is the minimum (e.g., INT_MIN for int type).

Link: https://lkml.kernel.org/r/20251106152051.2361551-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>