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

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

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Martijn Coenen <maco@android.com>
Cc: Greg Hartman <ghartman@google.com>
Cc: devel@driverdev.osuosl.org
Cc: kernel-team@android.com
Signed-off-by: Alistair Strachan <astrachan@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>