vfio/nvgrace-gpu: split the code to wait for GPU ready

vfio/nvgrace-gpu: split the code to wait for GPU ready

Split the function that check for the GPU device being ready on
the probe.

Move the code to wait for the GPU to be ready through BAR0 register
reads to a separate function. This would help reuse the code.

This also fixes a bug where the return status in case of timeout
gets overridden by return from pci_enable_device. With the fix,
a timeout generate an error as initially intended.

Fixes: d85f69d520e6 ("vfio/nvgrace-gpu: Check the HBM training and C2C link status")
Reviewed-by: Zhi Wang <zhiw@nvidia.com>
Reviewed-by: Shameer Kolothum <skolothumtho@nvidia.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20251127170632.3477-5-ankita@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>