afs: Pass page into dirty region helpers to provide THP size

Pass a pointer to the page being accessed into the dirty region helpers so
that the size of the page can be determined in case it's a transparent huge
page.

This also required the page to be passed into the afs_page_dirty trace
point - so there's no need to specifically pass in the index or private
data as these can be retrieved directly from the page struct.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/160588527183.3465195.16107942526481976308.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118144921.1232039.11377711180492625929.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161040747.2537118.11435394902674511430.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340404553.1303470.11414163641767769882.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539548385.286939.8864598314493255313.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653804285.2770958.3497360004849598038.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789087043.6155.16922142208140170528.stgit@warthog.procyon.org.uk/ # v6