lib: polynomial: move to math/ subfolder

lib: polynomial: move to math/ subfolder

Patch series "lib: polynomial: Move to math/ and clean up", v2.

While removing Baikal SoC and platform code pieces I found that this code
belongs to lib/math/ rather than generic lib/.  Hence the move and
followed up cleanups.

This patch (of 3):

The algorithm behind polynomial belongs to our collection of math
equations and expressions handling.  Move it to math/ subfolder where
others of the kind are located.

Link: https://lkml.kernel.org/r/20260302092831.2267785-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>