uuid: hoist helpers uuid_equal() and uuid_copy() from xfs

These helper are used to compare and copy two uuid_t type objects.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
[hch: also provide the respective guid_ versions]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>