tests: fixed blacklisting for UART tests

changed from explicit blacklisting to feature based approach
boards: added missing UART feature

added for:
- airfy-beacon
- arduino-mega2560
- cc2538dk
- msbiot
- openmote
- pca1000[0|5]
- spark-core
- stm32f4discovery
- yunjia-nrf51822
board/mbed_lpc1768: added UART configuration
cpu/lpc1768: added basic UART driver
board/mbed_lpc1768: changed binary ouput to .bin
Merge pull request #2171 from haukepetersen/fix_mbed_binfile

board/mbed_lpc1768: changed binary ouput to .bin
Merge pull request #2165 from haukepetersen/fix_test_uart

test/periph_uart_xx: switched to feature based whitelisting
board/mbed_lpc1768: added flash script
Merge pull request #2167 from haukepetersen/add_lpc1768_uart

cpu/lpc1768: added basic UART driver
Merge pull request #2172 from haukepetersen/add_mbed_makeflash

board/mbed_lpc1768: added flash script