x86/PCI: Add pci_numachip_init() declaration

x86/PCI: Add pci_numachip_init() declaration

numachip.c defines pci_numachip_init(), but neglected to include its
declaration, causing the following sparse and compile time warnings:

  arch/x86/pci/numachip.c:108:12: warning: no previous prototype for function 'pci_numachip_init' [-Wmissing-prototypes]
  arch/x86/pci/numachip.c:108:12: warning: symbol 'pci_numachip_init' was not declared. Should it be static?

Include asm/numachip/numachip.h, which includes the missing declaration.

Link: https://lore.kernel.org/r/20210812171717.1471243-1-kw@linux.com
Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>