iris: Drop usage of i915 EXEC_OBJECT_WRITE

iris: Drop usage of i915 EXEC_OBJECT_WRITE

The whole usage of this flag is to call iris_use_pinned_bo() with
writable argument, for that we don't need any i915_drm.h specific type.
IRIS_BLORP_RELOC_FLAGS_EXEC_OBJECT_WRITE could have any other value but
keeping the same as i915_drm.h.

With this we can drop 2 i915_drm.h imports from generic Iris code.

Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21887>