rtc: rv3029: Add support of RV3049

Add support of Microcrystal RV3049 RTC (SPI) using regmap on the
RV3029 (I2C) driver.

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>