This renames e31x_rfnoc_image_core.* to e310_rfnoc_image_core.*. This
makes the naming consistent with the rest of the build process (which
uses "e310" for all variants of e31x) and fixes an issue in which the
wrong file name was used by rfnoc_image_builder.
Original-commit: bbd43b16e18ef0a0311ddf4635cbd29c4ac3c367
Wade Fife
f1d3374e50