Add an RTC driver for the RTC device on Ricoh MFD RC5T619,
which is implemented as a variant of RN5T618.

rtc-range output:
Testing 2000-02-28 23:59:59.
OK

Testing 2038-01-19 03:14:07.
OK

Testing 2069-12-31 23:59:59.
OK

Testing 2099-12-31 23:59:59.
KO RTC_RD_TIME returned 22 (line 138)

Testing 2100-02-28 23:59:59.
KO RTC_SET_TIME returned 34 (line 122)

Testing 2106-02-07 06:28:15.
KO RTC_SET_TIME returned 34 (line 122)

Testing 2262-04-11 23:47:16.
KO RTC_SET_TIME returned 34 (line 122)
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>