PCI: designware-ep: Fix DBI access before core init

Platforms that cannot support their core initialization without the
reference clock from the host, implement the feature 'core_init_notifier'
to indicate the DesignWare sub-system about when their core is getting
initialized. Any accesses to the core (Ex:- DBI) would result in system
hang in such systems (Ex:- tegra194). This patch moves any access to the
core to dw_pcie_ep_init_complete() API which is effectively called only
after the core initialization.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
[mani: moved edma and ep_init to init_complete callback]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>