boards: arm: frdm_k82f: add support for the NXP FRDM-K82F board

Add support for the NXP FRDM-K82F development board. This board
features an NXP MK82FN256VLL15 CPU, a user RGB LED and two buttons,
two 32 Mb QSPI flashes, Arduino R3 compatible headers, and a FlexIO
header.

Signed-off-by: Filip Brozovic <fbrozovic@gmail.com>