boards: added support for OpenMote

rebased on #1861, #1862 and #1863 
This looks a bit like change for the sake of change. Also, it will produce the wrong vector table if any of the following is true:

UART_0_DEV != UART_0
UART_1_DEV != UART_1
TIMER_0_DEV != GPTIMER0
TIMER_1_DEV != GPTIMER1
TIMER_2_DEV != GPTIMER2
TIMER_3_DEV != GPTIMER3