ppc/pnv: set phb4 properties in stk_realize()

Moving all phb4 properties setup to stk_realize() keeps this logic in
a single place instead of having it scattered between stk_realize() and
pec_realize().

'phb->index' can be retrieved using stack->stack_no and
pnv_phb4_pec_get_phb_id(), deprecating the use of 'phb-id' alias that
was being used for this purpose in pec_realize().

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220111131027.599784-2-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>