fix(h700): dimmer low brightness and audible, quieter low volume

[SimoGecko]

Two fixes to the H700 (Anbernic) libmsettings, reported on an RG SP.

Brightness levels 0-3 are too bright in the dark

The disp driver sets the backlight PWM duty to (raw+1)/256 and raw 0 turns the backlight off, so the old floor (raw 4) was not the dimmest lit level. Levels 0-3 now use raw 1/3/7/15, a duty of 2/4/8/16 out of 256, doubling each step. Level 0 is about 2.5x dimmer than before. Level 4 and up, and the default, are unchanged. muOS also uses raw 1 as its minimum on these devices.

Volume step 1 is silent and step 2 is already loud

The speaker path wrote percentages to the codec controls, and tinyalsa's truncation put step 1 on lineout volume raw 1. On the H616/H700 codec, lineout raw 0 and 1 are both mute (mainline sun6i_codec_lineout_vol_scale: 0-1 mute, 2-31 is -43.5 dB to 0 dB in 1.5 dB steps). Step 2 then landed on raw 3, -42 dB.

This replaces the percentages with an explicit {lineout, digital} table per step:

• Lineout rises by one every step from raw 2, so no non-zero step is muted.
• Steps 1-5 add digital volume attenuation (1.16 dB per raw step) to reach about -55 dB at step 1.
• Digital stays at 0 dB from step 6 up, and the mid and upper steps stay within about 3 dB of the old levels.
• The Bluetooth and USB DAC paths are unchanged.

Open question

With the old mapping, step 2 should have been about -107 dB in total (lineout -42 dB plus digital raw 56, about -65 dB), yet it is clearly audible on the RG SP. That suggests digital volume may not attenuate on this unit. If so, steps 1-5 only reach lineout's -43.5 dB to -37.5 dB, but each step is still audible and distinct. Running amixer sset 'digital volume' 30 during playback would confirm it either way.

Testing

• Build and test on an RG SP (draft until this is done)
• Checked the dB value of every table entry with a script

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