boards: 96b_argonkey: adapt to the board configuration guidelines

As per default board configuration guidelines, this commit updates
96Boards Argonkey board.

Following changes are done:

- Enable exposed SPI1
- Update yaml file
- Only enable basic peripherals in board defconfig
- Add exposed peripherals in board Kconfig

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>