PCI: Remove MPS/MRRS Kconfig settings (CONFIG_PCIE_BUS_*)

Revert b0e85c3c8554 ("PCI: Add Kconfig options for MPS/MRRS strategy"),
which allowed build-time selection of the "off", "default", "safe",
"performance", or "peer2peer" strategies for MPS and MRRS configuration.
These strategies can be selected at boot-time using the
"pci=pcie_bus_tune_*" kernel parameters.

Per the discussion mentioned below, these Kconfig options were added to
work around a hardware defect in a WiFi device used in a cable modem.  The
defect occurred only when the device was configured with MPS=128, and
Kconfig was a way to avoid that setting.  It was easier for the modem
vendor to use Kconfig and update the kernel image than to change the kernel
parameters.

Neither Kconfig nor kernel parameters are a complete solution because the
broken WiFi device may be used in other systems where it may be configured
with MPS=128 and be susceptible to the defect.

Remove the Kconfig settings to simplify the MPS code.  If we can identify
the WiFi device in question, we may be able to make a generic quirk to
avoid the problem on all system.

This is not a fix and should not be backported to previous kernels.

Link: https://lore.kernel.org/all/CA+-6iNzd0RJO0L021qz8CKrSviSst6QehY-QtJxz_-EVY0Hj0Q@mail.gmail.com
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260326221311.1356180-1-bhelgaas@google.com

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