leds: mt6370: Annotate struct mt6370_priv with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct mt6370_priv.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230915201051.never.429-kees@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>

leds: flash: mt6370: Add MediaTek MT6370 flashlight support

The MediaTek MT6370 is a highly-integrated smart power management IC,
which includes a single cell Li-Ion/Li-Polymer switching battery
charger, a USB Type-C & Power Delivery (PD) controller, dual Flash
LED current sources, a RGB LED driver, a backlight WLED driver,
a display bias driver and a general LDO for portable devices.

Add support for the MT6370 Flash LED driver. Flash LED in MT6370
has 2 channels and support torch/strobe mode.

Co-developed-by: Alice Chen <alice_chen@richtek.com>
Signed-off-by: Alice Chen <alice_chen@richtek.com>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/52480420a160e5a4c71715fbbf105e684a16e7c2.1678430444.git.chiaen_wu@richtek.com