Fixed baudrate calculation issue in serial_api.c, arduino compatible pins name and USB device for Freescale KL43Z Target
Added serial_get_src_clock() function into serial_api.c and fastirc_frequency() function into clk_freqs.h for better portability.
Merge pull request #805 from molejar/dev-freescale-kl43z

Targets: KL43Z - Fix some issues in serial, usb device and pins names