Add serialization methods to whitelist not light greylist

Checked the contents of the hiddenapi lists before and after the change
and the methods were definitely moved from light greylist to the
whitelist.

Flashed the device and checked the log and did not see anything out of
the ordinary.

Test: frameworks/base/tools/hiddenapi/generate_hiddenapi_lists_test.py
Change-Id: I9b4b2426251e99495f65ae02a3c2c32ce6966625