PCI/ASPM: Remove PCIEASPM_DEBUG Kconfig option and related code

Previously, CONFIG_PCIEASPM_DEBUG enabled "link_state" and "clk_ctl" sysfs
files that controlled ASPM.  We believe these files were rarely if ever
used.

We recently added sysfs ASPM controls that are always present, so the debug
code is no longer needed.  Removing this debug code has been discussed for
quite some time, see e.g. [0].

Remove PCIEASPM_DEBUG and the related code.

[0] https://lore.kernel.org/lkml/20180727202619.GD173328@bhelgaas-glaptop.roam.corp.google.com/
Link: https://lore.kernel.org/r/ec935d8e-c084-3938-f1d1-748617596b25@gmail.com


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