powerpc/ptdump: Refactor update of pg_state

In note_page(), the pg_state is updated the same way in two places.

Add note_page_update_state() to do it.

Also include the display of boundary markers there as it is missing
"no level" leg, leading to a mismatch when the first two markers
are at the same address and the first displayed area uses that
address.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a284a809f01c705bbaab303b06fda216f147a99a.1593429426.git.christophe.leroy@csgroup.eu