PCI/sysfs: Convert "config" to static attribute

The "config" sysfs attribute allows access to either the legacy (PCI and
PCI-X Mode 1) or the extended (PCI-X Mode 2 and PCIe) device configuration
space.  Previously it was dynamically created either when a device was
added (for hot-added devices) or via a late_initcall (for devices present
at boot):

  pci_bus_add_devices
    pci_bus_add_device
      pci_create_sysfs_dev_files
        if (!sysfs_initialized)
	  return
	sysfs_create_bin_file           # for hot-added devices

  pci_sysfs_init                        # late_initcall
    sysfs_initialized = 1
    for_each_pci_dev(pdev)
      pci_create_sysfs_dev_files(pdev)  # for devices present at boot

And dynamically removed when the PCI device is stopped and removed:

  pci_stop_bus_device
    pci_stop_dev
      pci_remove_sysfs_dev_files
        sysfs_remove_bin_file

This attribute does not need to be created or removed dynamically, so we
can use a static attribute so the device model takes care of addition and
removal automatically.

Convert "config" to a static attribute and use the .is_bin_visible()
callback to set the correct object size (either 256 bytes or 4 KiB) at
runtime.

The pci_sysfs_init() scheme was added in the pre-git era by
https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/drivers/pci/pci-sysfs.c?id=f6d553444da2



[bhelgaas: commit log]
Suggested-by: Oliver O'Halloran <oohall@gmail.com>
Link: https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqaA@mail.gmail.com
Link: https://lore.kernel.org/r/20210416205856.3234481-2-kw@linux.com


Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>