This function will be used in lib/crypto/x509_cert_parser.c, which
will also be imported from linux code in a later commit.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
In the next commit, rtc_mktime(), for compatibility with linux, will be
implemented using rtc_mktime(), which is no longer drivers/rtc specific.
So move this file under lib/.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>