PCI: dra7xx: Use threaded IRQ handler for "dra7xx-pcie-main" IRQ

The "dra7xx-pcie-main" hard IRQ handler is just printing the IRQ status
and calling the dw_pcie_ep_linkup() API if LINK_UP status is set. But the
execution of dw_pcie_ep_linkup() depends on the EPF driver and may take
more time depending on the EPF implementation.

In general, hard IRQ handlers are supposed to return quickly and not block
for so long. Moreover, there is no real need of the current IRQ handler to
be a hard IRQ handler. So switch to the threaded IRQ handler for the
"dra7xx-pcie-main" IRQ.

Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>