drm/xe: Fix unmet direct dependencies warning

drm/xe: Fix unmet direct dependencies warning

WARNING: unmet direct dependencies detected for FB_IOMEM_HELPERS
  Depends on [n]: HAS_IOMEM [=y] && FB_CORE [=n]
  Selected by [m]:
  - DRM_XE_DISPLAY [=y] && HAS_IOMEM [=y] && DRM [=m] && DRM_XE [=m] && DRM_XE [=m]=m [=m] && HAS_IOPORT [=y]

DRM_XE_DISPLAY requires FB_IOMEM_HELPERS, but the dependency FB_CORE is
missing, selecting FB_IOMEM_HELPERS if DRM_FBDEV_EMULATION is set as
other drm drivers.

Fixes: 44e694958b95 ("drm/xe/display: Implement display support")
Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250323114103.1960511-1-yuehaibing@huawei.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>