PCI: imx6: Separate PERST# assertion from core reset functions

PCI: imx6: Separate PERST# assertion from core reset functions

The imx_pcie_assert_core_reset() and imx_pcie_deassert_core_reset()
functions are primarily intended to reset the RC controller itself, not
the remote PCIe endpoint devices. However, the PERST# GPIO control was
previously embedded within these functions, which conflates two distinct
reset operations.

Move the PERST# GPIO handling into a dedicated function
imx_pcie_assert_perst(). This makes the code more maintainable and
prepares for parsing the reset-gpios property according to the new
Root Port DT binding in subsequent patches.

No functional change is intended.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Richard Zhu <hongxing.zhu@nxp.com>
Link: https://patch.msgid.link/20260306030456.1032815-1-sherry.sun@nxp.com