PCI/VPD: Add pci_vpd_find_ro_info_keyword()

All users of pci_vpd_find_info_keyword() are interested in the VPD RO
section only. In addition all calls are followed by the same activities to
calculate start of tag data area and size of the data area.

Add pci_vpd_find_ro_info_keyword() that combines these functionalities.

pci_vpd_find_info_keyword() can be phased out once all users are converted.

[bhelgaas: split pci_vpd_check_csum() to separate patch]
Link: https://lore.kernel.org/r/1643bd7a-088e-1028-c9b0-9d112cf48d63@gmail.com


Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>