sparc64/mm: Implement pXX_leaf_size() support

Sparc64 has non-pagetable aligned large page support; wire up the
pXX_leaf_size() functions to report the correct pagetable page size.

This enables PERF_SAMPLE_{DATA,CODE}_PAGE_SIZE to report accurate
pagetable leaf sizes.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201126121121.301768209@infradead.org