packaging/kernel: Add CONFIG_PCI_MMCONFIG to x86 guest kernel configu…

…ration

The guest kernel configuration suggested for Kata, and which is used by the
CI didn't include CONFIG_PCI_MMCONFIG.  That's kind of weird, MMCONFIG is
the modern normal way of handling configuration cycles.

In addition, due to a complex set of interactions through the ACPI code,
disabling MMCONFIG means that SHPC hotplug doesn't work: the driver is
included in the guest kernel, but will fail to probe on PCI to PCI bridges,
meaning it won't actually be activated.

Enable MMCONFIG so that we suggest and testa more typical guest kernel
configuration.

fixes #2288

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tools/packaging/kernel/configs/fragments/x86_64/pci.conf

@@ -1 +1,2 @@
+CONFIG_PCI_MMCONFIG=y
 CONFIG_PCI_MSI_IRQ_DOMAIN=y