PCI: spear: Rename add_pcie_port(), pcie_init() to spear13xx_add_pcie_port(), etc.

The add_pcie_port() and pcie_init() functions are SPEAr13xx-specific.  Add
spear13xx prefix to avoid collision in global name space.

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