FROMLIST: staging: vsoc: Create wc kernel mapping for region shm.

Map the region shm as write-combining instead of uncacheable.

Signed-off-by: Alistair Strachan <astrachan@google.com>
[sent upstream via staging TODO]
Bug: 702147120
Change-Id: If587b4f26abaa3580b889b04dbb655f8d5b4a8ee