Use functions provided by drivers/pci/ecam.h for mapping the config space
in drivers/pci/host/pci-host-common.c, and update its users to use 'struct
pci_config_window' and 'struct pci_ecam_ops'.

The changes are mostly to use 'struct pci_config_window' in place of
'struct gen_pci'.  Some of the fields of gen_pci were only used temporarily
and can be eliminated by using local variables or function arguments, these
are not carried over to struct pci_config_window.

pci-thunder-ecam.c and pci-thunder-pem.c are the only users of the
pci_host_common_probe function and the gen_pci structure; these have been
updated to use the new API as well.

The patch does not introduce any functional changes other than a very minor
one: with the new code, on 64-bit platforms, we do just a single ioremap
for the whole config space.
Signed-off-by: NJayachandran C <jchandra@broadcom.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

Add config option PCI_ECAM and file drivers/pci/ecam.c to provide generic
functions for accessing memory-mapped PCI config space.

The API is defined in drivers/pci/ecam.h and is written to replace the API
in drivers/pci/host/pci-host-common.h.  The file defines a new 'struct
pci_config_window' to hold the information related to a PCI config area and
its mapping.  This structure is expected to be used as sysdata for
controllers that have ECAM based mapping.

Helper functions are provided to setup the mapping, free the mapping and to
implement the map_bus method in 'struct pci_ops'
Signed-off-by: NJayachandran C <jchandra@broadcom.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>