FreeBSD 12.0 RBPI3B+ and hardware clock support

[Stefan Parvu]

> 
> My link was to the file's page on GitHub, not direct download and it
> looks like you donwloaded HTML instead of the dtbo, the correct link is:
> https://github.com/raspberrypi/firmware/raw/master/boot/overlays/i2c-rtc.dtbo
> The size is 3934 and MD5 checksum is 6d8217ed669f61c0dfb7b985696a540c

gee. silly me. let me fetch the correct file.