platform/x86: x86-android-tablets: Fix backlight ctrl for Lenovo Yoga Tab 3 Pro YT3...

platform/x86: x86-android-tablets: Fix backlight ctrl for Lenovo Yoga Tab 3 Pro YT3-X90F

Fix the maximum brightness being much too low on the Yoga Tab 3 Pro.

The LP8557 backlight controller can either be configured to multiply its
PWM input and the I2C register set level (requiring both to be at 100%
for 100% output); or to only take the I2C register set level into account.

Multiplying the 2 levels is useful because this will turn off the backlight
when the panel goes off and turns off its PWM output.

But on the YT3-X90F the panel's PWM output defaults to a duty-cycle of much
less then 100%, severely limiting max brightness. In this case the LP8557
should be configured to only take the I2C register into account and
the i915 driver must turn off the backlight separately using a VBT MIPI
sequence to turn off the backlight.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20231104205828.63139-4-hdegoede@redhat.com