Powerpc: T208xQDS: Modify the comment of the CONFIG_FSL_PCIE_RESET macro

Remove duplicate macro CONFIG_FSL_PCIE_RESET and update its comment.
It enables PCIe reset to fix link width 2x - 4x.

Signed-off-by: Bao Xiaowei <xiaowei.bao@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>