boards: initial import of yunjia-nrf51822 board
cpu/nrf51822: some fixes and clean up

- enabled power for uart and timer
- outsourced timer config values to periph_conf.h
- made linkerscript better readable
- adjusted default stack-sizes
- let RED_LED blink on hard_fault
board/pca1000x: small fixes to periph_conf.h files
tests/examples: blacklisted yunjia-nrf51822