Unify timer code

Remove the timer and TSC additional input code and instead provide a single
routine that attempts to use the "best" timer/counter available on the
system.  It attempts to use TSC, then various OS dependent resources and
finally several tries to obtain the date.  If any of these timer/counters
is successful, the rest are skipped.

No randomness is credited for this.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/5231)