I just did a fresh clone and test build and was unable to replicate the BL2 image bloat you were seeing. However on my test machine I found that this patch was causing my machine to not boot from the usdhc card. Can you try and revert this commit from your build/rcw and test the image again?
lx2160acex7: mode 8: use external PLLs
If you are still having the bloat issue I can also share my patch that switches to gcc-10