Sorry for the necro. Maybe this will help someone else trying to run this nvme on an older board…
I have a dell with one of these kioxia bg4 drives (512gb). Wanted to put an nvme in an old gigabyte z97, so figured I’d do some drive swapping. Got a wd sn570 that works just fine with the z97, but it won’t boot with the bg4. Adding NvmExpressDxe_5.ffs (from [HowTo] Get full NVMe Support for all Systems with an AMI UEFI BIOS ) to the bios resolved the issue. Using it with a pcie adapter gets the full pcie2.0 x4 supported by the z97 (vs pcie2.0 x2 via m2). Haven’t tested bifurcating the cpu’s pcie3.0 but imagine it’d be fine too.
Tested the sn570 and it still works fine with the bios having both oem nvme support and the added dxe driver. Would it make sense to try streamlining by updating the existing dxe drivers with ones from a newer board-bios (z170 perhaps) instead?