cpu/arm/k60: Add configurable parameter for debug UART baud rate.

The parameter K60_DEBUG_BAUD in config-board.h is used in the UART
driver to determine the correct divisor and fine adjust parameters
for the UART1 module.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Split UART SBR, BRFA from uart.c

Defined as macro functions UART_SBR, UART_BRFA in K60.h now.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Clean up udelay implementation.

Use F_BUS to compute the right timer value when waiting.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>