ANDROID: PCI: dwc: export symbols for ep driver

Export symbols for building Designware PCIe EP driver as kernel module.
Partially cherry-picked for EXPORT_SYMBOL_GPL part from below patch.

c57247f940e8 ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")

Bug: 167931570
(partial backport of commit c57247f940e8ea13a0ec33378304dc3cdc5da4a8.
 Didn't backport entier patch because it requires below two precedence
 patchset to avoid patch conflict.
 "Add support to defer core initialization" by Vidya
 "Improvements to PCIe Endpoint Core" by Kishon)
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Change-Id: I4df622d67d4202c650abff6c424d1e3cb30408e2