fix:

 arch/x86/kernel/built-in.o: In function `nvidia_set_debug_port':
 early_printk.c:(.text+0xf8b1): undefined reference to `read_pci_config'
 early_printk.c:(.text+0xf8dc): undefined reference to `write_pci_config'
 arch/x86/kernel/built-in.o: In function `setup_early_printk':
 early_printk.c:(.init.text+0x5487): undefined reference to `early_pci_allowed'
 early_printk.c:(.init.text+0x54cb): undefined reference to `read_pci_config'
 early_printk.c:(.init.text+0x54ec): undefined reference to `read_pci_config_16'
 [...]
Signed-off-by: NIngo Molnar <mingo@elte.hu>