drm/i915: Do not set cache_dirty for DGFX

Currently on DG1, which does not have LLC, we hit the below
warning while rebinding an userptr invalidated object.

WARNING: CPU: 4 PID: 13008 at drivers/gpu/drm/i915/gem/i915_gem_pages.c:34 __i915_gem_object_set_pages+0x296/0x2d0 [i915]
...
RIP: 0010:__i915_gem_object_set_pages+0x296/0x2d0 [i915]
...
Call Trace:
 <TASK>
 i915_gem_userptr_get_pages+0x175/0x1a0 [i915]
 ____i915_gem_object_get_pages+0x32/0xb0 [i915]
 i915_gem_object_userptr_submit_init+0x286/0x470 [i915]
 eb_lookup_vmas+0x2ff/0xcf0 [i915]
 ? __intel_wakeref_get_first+0x55/0xb0 [i915]
 i915_gem_do_execbuffer+0x785/0x21d0 [i915]
 i915_gem_execbuffer2_ioctl+0xe7/0x3d0 [i915]

We shouldn't be setting the obj->cache_dirty for DGFX,
fix it.

Fixes: d70af579 ("drm/i915/shmem: ensure flush during swap-in on non-LLC")
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Reported-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221102051416.27327-1-niranjana.vishwanathapura@intel.com