sb/intel/common/pciehp: Replace HP dummy device with common code

Use the common PCIEXP_HOTPLUG code to generate a dummy device for PCIe
ports supporting hotplug. This allows to have control over how much
resources are allocated to hotplug ports.

Tested on thinkpad X220: now hotplugging a dGPU via the expresscard
slot sometimes works.

Change-Id: I3eec5214c9d200ef97d1ccfdc00e8ea0ee7cfbc6
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51068
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Patrick Rudolph
diff --git a/src/southbridge/intel/i82801ix/Kconfig b/src/southbridge/intel/i82801ix/Kconfig
index 3ee2943..992562f 100644
--- a/src/southbridge/intel/i82801ix/Kconfig
+++ b/src/southbridge/intel/i82801ix/Kconfig
@@ -38,4 +38,7 @@
 	bool
 	default n
 
+config PCIEXP_HOTPLUG
+	default y
+
 endif