Like we have for other DATA_SETs already in uart, e.g.,
UART_FDT_CLASS_AND_DEVICE, name the newly created uart_class_set
DATA_SET as UART_CLASS(). This further hides the data set name.
Also add UART_CLASS for quicc, which was previously not done.
MFC after: 1 week
Improves: 949670f8f466 dev/uart: Use a linker set to find uart classes
Obtained from: https://github.com/freebsd/freebsd/commit/269e99ac86902127bfaee1500d8747a3c7be5912