RTC_Init will turn off the RTC and readout will not be possible until
RTC_EnableRTCE is called.  The previous version worked because the
bootloader would call RTC_Init and Epicardium would then call
RTC_EnableRTCE.

This broke with the hardware-init changes in

    b76ac8fc

and lead to behavior where cold boot would not enable the RTC.  This
commit switches the order of the two calls in the bootloader so it is
always initialized correctly.  Because some older bootloaders are
already out in the field, this commit also introduces basic rtc init
into Epicardium so the new firmware can work correctly with older
bootloaders.

Signed-off-by: Rahix <rahix@rahix.de>