modules: fix some riscv module logic

The change which enabled the sdhci_fdt module build on riscv
inadvertently enabled the neta module as well. This driver is not needed
on this platform.

Move each entry to a respective identical conditional blocks.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Fixes: e9dd9f95f82f ("riscv: Add the sdhci_fdt driver to the build")

(cherry picked from commit ddc1d4b0722bd63934f503c43a5ee35d871355ee)