Coldfire: Fix half-baud UART by adding M5271 to Coldfire v2 core list

Added the CONFIG_M5271 to the list of Coldfire V2 processor. This
was causing the bus clock (not CPU clock) to be declared twice as
fast as it actually is. This causes UARTS to operate at half the
specified baudrate.

Signed-off-by: Richard Retanubun <RichardRetanubun@RuggedCom.com>