PCI/ASPM: Clarify that pcie_aspm=off means leave ASPM untouched

Previously we claimed "pcie_aspm=off" meant that ASPM would be disabled,
which is wrong.

Correct this to say that with "pcie_aspm=off", Linux doesn't touch any ASPM
configuration at all.  ASPM may have been enabled by firmware, and that
will be left unchanged.  See "aspm_support_enabled".

Link: https://lore.kernel.org/r/20240429191821.691726-1-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: David E. Box <david.e.box@linux.intel.com>

Author: bjorn-helgaas

Documentation/admin-guide/kernel-parameters.txt

@@ -4590,9 +4590,10 @@
 		norid		[S390] ignore the RID field and force use of
 				one PCI domain per PCI function
 
-	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
+	pcie_aspm=	[PCIE] Forcibly enable or ignore PCIe Active State Power
 			Management.
-		off	Disable ASPM.
+		off	Don't touch ASPM configuration at all.  Leave any
+			configuration done by firmware unchanged.
 		force	Enable ASPM even on devices that claim not to support it.
 			WARNING: Forcing ASPM on may cause system lockups.