GKI cleanup - Moved GKI_get_os_tick_count() to OSI

 * Renamed function GKI_get_os_tick_count() to time_get_os_boottime_ms()
   and moved it to the OSI module: to the new file osi/src/time.c .
   The corresponding header file is osi/include/time.h

 * Added unit tests for function time_get_os_boottime_ms() in file
   osi/test/time_test.cpp

 * Removed "osi/include" from the list of paths to search for include
   files. This is needed, because file name collision of "time.h"
   in osi/include and the system <time.h>

Change-Id: I934be0c8f392150a352947326546bcf8aa070f97