This adds support for the LEGO Hub No. 7, aka LEGO Technic Small hub, aka
LEGO SPIKE Essential hub. This board is largely similar to Hub No. 6:
- Same MCU (STM32F413 - different packaging with fewer pins).
- Same Bluetooth chip (TI CC2564).
- Same IMU chip.
- Similar external flash chip - 4MiB instead of 32MiB.
- 2 I/O ports instead of 6.
- No display - only status and battery LEDs.
- Different LED driver chip.
- Only 1 button which is also the power button.
- No speaker.
Signed-off-by: David Lechner <david@pybricks.com>
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