uboot-imx

armv8: fsl-layerscape: Update parsing boot source

Workaround of erratum A010539 clears the RCW source field in PORSR1
register, causing failure of detecting boot source using this method.
Use SMC call if U-Boot runs at EL2. If SMC is not implemented or
running at EL3, continue to read PORSR1 and presume QSPI as boot
source if erratum workaround A010539 is enabled and RCW source is
cleared.

Signed-off-by: York Sun <york.sun@nxp.com>