hw/ppc: Add pnv nest pervasive common chiplet model

hw/ppc: Add pnv nest pervasive common chiplet model

A POWER10 chip is divided into logical units called chiplets. Chiplets
are broadly divided into "core chiplets" (with the processor cores) and
"nest chiplets" (with everything else). Each chiplet has an attachment
to the pervasive bus (PIB) and with chiplet-specific registers. All nest
chiplets have a common basic set of registers and This model will provide
the registers functionality for common registers of nest chiplet (Pervasive
Chiplet, PB Chiplet, PCI Chiplets, MC Chiplet, PAU Chiplets)

This commit implement the read/write functions of chiplet control registers.

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Chalapathi V <chalapathi.v@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>