A number of architectures have non-pagetable aligned huge/large pages.
For such architectures a leaf can actually be part of a larger entry.

Provide generic helpers to determine the size of a page-table leaf.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lkml.kernel.org/r/20201126121121.102580109@infradead.org