hx20: FP_LED_LEVEL_CONTROL takes symbolic inputs but returns raw outputs

[DHowett]

Calling the FP_LED_LEVEL_CONTROL host command with set requires one of the symbolic LED brightnesses:

• FP_LED_BRIGHTNESS_HIGH = 0
• FP_LED_BRIGHTNESS_MEDIUM = 1
• FP_LED_BRIGHTNESS_LOW = 2

However, calling it with get populated returns the actual stored brightness value:

• high = 55 (FP_LED_HIGH)
• medium = 40 (FP_LED_MEDIUM)
• low = 15 (FP_LED_LOW)

### Write brightness 2 (low)
# ectool raw 0x3e0e b2,b0
3e0e(...2 bytes...)
 02 00                                           |..              |

### Read back (low = 15)
# ectool raw 0x3e0e b0,b1
3e0e(...2 bytes...)
 00 01                                           |..              |
Read 1 bytes
 0f                                              |.               |

[hauntingEcho]

It looks like the relevant code is here: https://github.com/FrameworkComputer/EmbeddedController/blob/hx20/board/hx20/led.c#L400