PCI: Rename _DSM constants to align with spec

Rename PCI-related _DSM constants to align them with the PCI Firmware Spec,
r3.2, sec 4.6.  No functional change intended.

Link: https://lore.kernel.org/r/20200526213905.2479381-1-kw@linux.com


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