Add zephyr framework to lpcxpresso55s69

[anujdeshpande]

I made changes based on the similar 55S16 board file here. First commit here, so let me know if there's something missing!

Also, there's 2 additional variants for the board under zephyr

• lpcxpresso55s16_cpu0
• lpcxpresso55s16_cpu1

As I understand, I'll have to create different board files for these variants?

[anujdeshpande]

cc @valeros @ivankravets