x86/jailhouse: Respect pci=lastbus command line settings

Limiting the scan width to the known last bus via the command line can
accelerate the boot noteworthy.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Jailhouse <jailhouse-dev@googlegroups.com>
Link: https://lkml.kernel.org/r/51f5fe62-ca8f-9286-5cdb-39df3fad78b4@siemens.com

arch/x86/kernel/jailhouse.c

@@ -119,8 +119,10 @@ static int __init jailhouse_pci_arch_init(void)
 	/*
 	 * There are no bridges on the virtual PCI root bus under Jailhouse,
 	 * thus no other way to discover all devices than a full scan.
+	 * Respect any overrides via the command line, though.
 	 */
-	pcibios_last_bus = 0xff;
+	if (pcibios_last_bus < 0)
+		pcibios_last_bus = 0xff;
 
 	return 0;
 }