drm/v3d: Reach the GMP through the hub registers on V3D 7.x

drm/v3d: Reach the GMP through the hub registers on V3D 7.x

v3d_idle_axi() drains the GPU's memory interface for a safe powerdown by
using the V3D_GMP_CFG register. It reached both registers with the macros
V3D_CORE_READ and V3D_CORE_WRITE.

On V3D 7.x the GMP is no longer a per-core block; it lives in the hub
register region. Reaching it through the per-core register block addresses
the wrong region.

Select the hub accessors (V3D_{READ,WRITE}) for the GMP on V3D 7.x and
keep the per-core path for earlier generations.

Cc: stable@vger.kernel.org
Fixes: 0ad5bc1ce463 ("drm/v3d: fix up register addresses for V3D 7.x")
Link: https://patch.msgid.link/20260718-v3d-pm-axi-transactions-v1-1-4ecd7729ed70@igalia.com
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>