pnv_phb4_pec: Move pnv_phb4_get_pec() to rightful file

pnv_phb4_pec: Move pnv_phb4_get_pec() to rightful file

The function pnv_phb4_get_pec() exposes some internals of the PEC and
PHB logic, yet it was in the higher level hw/ppc/pnv.c file for
historical reasons: P8 implements the PHBs from pnv.c directly, but on
P9/P10, it's done through the CEC model, which has its own file. So
move pnv_phb4_get_pec() to hw/pci-host/pnv_phb4_pec.c, where it fits
naturally.

While at it, replace the PnvPHB4 parameter by the PnvPHB front-end,
since it has all the information needed and simplify it a bit.

No functional changes.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Message-Id: <20230302163715.129635-4-fbarrat@linux.ibm.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>