drm/xe: s/lmem/vram/

This seems to be the preferred nomenclature in xe. Currently we are
intermixing vram and lmem, which is confusing.

v2 (Gwan-gyeong Mun & Lucas):
  - Rather apply to the entire driver

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>