Add fake_timerfd so time is deterministic in fuzz tests

Has same interface as timerfd with 2 additional functions:

fake_timerfd_reset(), to reset everything after a test.
fake_timerfd_advance(ms), to move time forward a number of ms.

Test: fuzz/run --host bluetooth_gd_hci_fuzz_test
Change-Id: Ifedada770797b014d08e439cb1915f4e733697e6