backlight: cr_bllcd: Introduce gpio-backlight semantics
cr_bllcd can turn backlight ON or OFF.
Fix semantitics so they equals what we know from gpio-backlight.
brightness == 0 => backlight off
brightness == 1 => backlight on
Use the backlight_get_brightness() helper to simplify the code.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
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