kernel/resource: Make ioport_resource.start configurable

Make IO space base address to be configurable through IO_SPACE_BASE.

This will allow architectures which do not natively support IO ports -
like arm64 - to harden against legacy ISA-based drivers which use
hardcoded addresses to access IO ports.

Any attempts for these drivers to request a resource region will now fail
for architectures with set IO_SPACE_BASE above legacy ISA IO port region
(0xffff).

Signed-off-by: John Garry <john.garry@huawei.com>

kernel/resource.c

@@ -29,7 +29,7 @@
 
 struct resource ioport_resource = {
 	.name	= "PCI IO",
-	.start	= 0,
+	.start	= IO_SPACE_BASE,
 	.end	= IO_SPACE_LIMIT,
 	.flags	= IORESOURCE_IO,
 };