Move CFG read/write function for PCI-compatible Configuration Mechanism from
debug/uartuart16550.c to hw/pci.c and rename CFG read/write function for
PCI-compatible Configuration Mechanism to pci_pio_read/write_cfg to align with
CFG read/write function pci_mmcfg_read/write_cfg for PCI Express Enhanced
Configuration Access Mechanism.
Tracked-On: #4371
Signed-off-by: Li Fei1 <fei1.li@intel.com>