drm/nouveau/bios: skip the IFR header if present

drm/nouveau/bios: skip the IFR header if present

The GPU's ROM may begin with an Init-from-ROM (IFR) header that precedes
the PCI Expansion ROM images (VBIOS).  When present, the PROM shadow
method must parse this header to determine the offset where the PCI ROM
images actually begin, and adjust all subsequent reads accordingly.

On most GPUs this is not needed because either the PRAMIN shadow method
(which reads from VRAM via the display engine) succeeds first, or the IFR
microcode has already applied the ROM offset so that PROM reads
transparently skip the header.  However, on GA100 neither of these
applies: GA100 has no display engine (so PRAMIN is unavailable), and the
IFR offset is not applied to PROM reads on this GPU.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260430223838.2530778-9-ttabi@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>