PCI: spear: Remove module option

We get the following error when built as a module. Though the general fix
would be in this case to export the below mentioned symbols, considering
that dw_pcie_host_init() is marked with __init and other PCI drivers do not
support modular build, I have disabled building this driver as a module
too.

  ERROR: "dw_pcie_host_init" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_handle_msi_irq" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_pcie_msi_init" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_pcie_cfg_write" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_pcie_cfg_read" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_pcie_setup_rc" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  ERROR: "dw_pcie_link_up" [drivers/pci/host/pcie-spear13xx.ko] undefined!
  make[1]: *** [__modpost] Error 1
  make: *** [modules] Error 2

Signed-off-by: Sachin Kamat <sachin.kamat@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>