x86: Permit PCI capability writes until we moderate them

9f49a9b899 blocks any write access to the PCI config space that is not
explicitly allowed. This includes capabilities which we need to properly
moderate (or even virtualize: MSI[-X]) later on. For now we need to
permit caps access again as machines will otherwise break too easily
over "Invalid PIO write".

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
inmates: Initialized SPIV APIC register

Do not rely on the previous user having left the APIC software-enabled
behind.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>