Document the MT6370 RGB LED pattern trigger.

This simply describe how the pattern works, each timing period, and the
pattern diagram for MT6370 RGB LED.
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/38f1e863b0f099158a63fb6f95056a1cb30d80a0.1678430444.git.chiaen_wu@richtek.com