PCI: dra7xx: Add __init annotation to dra7xx_add_pcie_port()

Add __init annotation to dra7xx_add_pcie_port(), because
dra7xx_add_pcie_port() is called only by dra7xx_pcie_probe() which is
marked __init.  This patch fixes a section mismatch warning:

WARNING: drivers/pci/host/built-in.o(.text.unlikely+0xcc): Section mismatch in reference from the function dra7xx_add_pcie_port() to the function .init.text:dw_pcie_host_init()

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>