The i.MX EP exhibits variations in epc_features among different EP
configurations. This introduces the addition of epc_features in
imx6_pcie_drvdata to accommodate these differences. It's important to note
that there are no functional changes in this commit; instead, it lays the
groundwork for supporting i.MX95 EP functions.

Link: https://lore.kernel.org/r/20240220161924.3871774-13-Frank.Li@nxp.comSigned-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>