It is impossible to get QSPI u-boot binary image with RCW by compiling u-boot source code.
You could download flexbuild_lsdk2012, run command "$ flex-builder -c rcw -m ls1046aqds" to get QSPI RCW binary file rcw_1600_qspiboot.bin.swapped in packages/firmware/rcw/ls1046aqds/RR_FFSNPPPH_1133_5559/. Please deploy RCW at 0x00000000, u-boot at 0x00100000 on QSPI flash