Fix ChibiOS backlight not turning off on suspend

[fauxpark]

Description

This is present in the AVR suspend code, but missing here.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[tzarc]

Will need to be rebased onto develop.
Cherry-picked it manually, works perfectly fine on actual hardware.

[fauxpark]

This is a bugfix, I think it should go into master.

[noroadsleft]

Slight __attribute__ ((weak)) ✔️ because I don't have any ChibiOS boards with backlighting.

[drashna]

did we want to import the rest of the code too? Eg, this:

qmk_firmware/tmk_core/common/avr/suspend.c

Lines 92 to 100 in 8937c14

	// Turn off LED indicators
	uint8_t leds_off = 0;
	# if defined(BACKLIGHT_CAPS_LOCK) && defined(BACKLIGHT_ENABLE)
	if (is_backlight_enabled()) {
	// Don't try to turn off Caps Lock indicator as it is backlight and backlight is already off
	leds_off |= (1 << USB_LED_CAPS_LOCK);
	}
	# endif
	led_set(leds_off);

Note, there doesn't seem to be any wake code (as it wouldn't actually be needed).

[fauxpark]

@drashna done

[tzarc]

LGTM, ship it.

[noroadsleft]

Thanks!