boards: arm: Add u-blox EVK-NINA-B4

Add support for u-blox EVK-NINA-B4, which uses the nRF52833

This board is similar to the nrf52833dk_nrf52833, though it
uses a u-blox NINA-B40x openCPU module with DC-DC support
included.
Simplified pwm LED aliases
Corrected LED assignments for red, green, and blue
Addressed review comments (spi & gpio 0 0)

Tested with blinky, button, and Bluetooth peripheral_hr

Signed-off-by: Bob Recny <bob.recny@u-blox.com>