Make LEDs work

[ikerperezdelpalomar]

• Add the code needed by leds from bloodlight-firmware
• Get it compiling with Zephyr GPIO APIs
• Add a main loop which goes through all the LEDs and toggles them on and off in order every second or so
• port bl_led_setup() and bl_led_loop().

[ikerperezdelpalomar]

I have ported all functions but bl_led_setup() and bl_led_loop().

I haven't ported bl_led_setup() because it's dependant of bl_acq_channel_get_source which is defined in src/acq and we haven't ported that yet.

I haven't ported bl_led_loop() because it is tightly related to spi code.

Therefore, this two functions will be ported once their dependencies are sorted.