MIPS: lantiq: Remove unused function pointer variables

Ever since introduction in the commit e47d4889 ("MIPS: Lantiq: Add
PCI controller support.") ltqpci_plat_dev_init has been unused. In
57c8cb8f ("MIPS: pci: convert lantiq driver to OF") also
ltq_pci_plat_arch_init was introduced.

With those commit being more than 10 years ago, it seem neither is
going to get used anytime soon. Thus, remove both unused function
pointer variables.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmal.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>