* Update rg_main.c
Added a menu to view and configure RTC parameters. It is activated by pressing 'TIME' button in retro-go main menu.
* Update main.c
Enable LSE oscillator and enable it as RTC clock source. Additionally enable CRS Sync LSE.
* Added time display to RTC menu
Added time display to RTC menu and also modified RTC initialization code so that it does not set the RTC date and time. Assuming that a fresh RTC has sensible values.
* Add date display to time menu
Added date display to time menu
* Fix predivs for LSE
Fixed predivs for LSE clock
* move RTC stuff to rg_rtc
Consolidate all RTC functions to rg_rtc. So far getters have been implemented only.
* Time setup UI + setters for Time
Setters for Time have been implemented and Time setup has been added into the UI to use them.
* Date setup added
Date setup with callbacks added
* Add real time datetime display
Modified the time menu to display and update in real time.
* Add a function to return Unix time
Unix time is returned as a 64-bit time_t. Casting to uint32_t will yield time in seconds since 1st Jan 1970.
* Fix setters' return type
Fixing warnings about wrong setter return type.
* Update rg_rtc.h
Missed the .h while updating return types of setters.
* Update rg_rtc.c
Add a nicer year display
* Reactivate LSI
This should fix an issue with DACs that causes Brightness control not to work.
