drm/i915/dg1: Fix mapping type for default state object

Use I915_MAP_WC when default state object is allocated in LMEM.

Signed-off-by: Venkata Ramana Nayana <venkata.ramana.nayana@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210427085417.120246-1-matthew.auld@intel.com