Add WearDisplayService to the system server;

add a SET_DISPLAY_OFFSET permission.

Merged-In: I253766553a507e2ada7d631501d8d32d863a823f

Bug: 36515029
Test: No build failure; SystemServer loads as usual.
Change-Id: I253766553a507e2ada7d631501d8d32d863a823f
(cherry picked from commit 069f46ca)