Fixes#6081
The SD rewrite blanked out some of the internal FAT info.. Restore the
function calls and return proper values.
Because size() is used in many printf()s, we can't just change its
return type to uint64. Instead, when size is > size-max warn.
Add SD.size64 which can be used by new apps who care about >4GB cards.
Prints a warning if debugging enabled
b5560759ec