boards: arm: 96b_nitrogen: Add 1.8v Low speed connector support

Add support for 1.8v Low speed connector available on the Wistrio
board inorder to access peripherals in a board independent way.

Following peripherals are supported:

1. 12-GPIOs
2. SPI0
3. UART0

Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>