drm/vc4: hvs: Rename hvs_regs list

The HVS register set has been heavily modified in the BCM2712, and we'll
thus need a separate debugfs_reg32 array for it.

The name hvs_regs is thus a bit too generic, so let's rename it to
something more specific.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>