T series boards use unified RCW for sd, spi and nand boot.
Now split txxx_rcw.cfg to txxx_sd_rcw.cfg, txxx_spi_rcw.cfg
and txxx_nand_rcw.cfg for SPI/NAND/SD boot.
And modify RCW[PBI_SRC] for them:
	PBI_SRC=5            for SPI 24-bit addressing
	PBI_SRC=6            for SD boot
	PBI_SRC=14           for IFC NAND boot
Signed-off-by: NZhao Qiang <qiang.zhao@nxp.com>
Reviewed-by: NYork Sun <york.sun@nxp.com>