kvm: Fix PCI config space emulation

kvm: Fix PCI config space emulation

This fixes the two problems:

  1. Yes, 'register number' is offset in 4 bytes, not 1 byte

  2. We must be able to return sane values for the whole 256 configuration
     space, not just for the first 64 bytes that's covered by the fixed header

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>