mm: replace xa_get_order with xas_get_order where appropriate

The tracing of invalidation and truncation operations on large files
showed that xa_get_order() is among the top functions where kernel spends
a lot of CPUs.  xa_get_order() needs to traverse the tree to reach the
right node for a given index and then extract the order of the entry. 
However it seems like at many places it is being called within an already
happening tree traversal where there is no need to do another traversal. 
Just use xas_get_order() at those places.

Link: https://lkml.kernel.org/r/20240906230512.124643-1-shakeel.butt@linux.dev


Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>