zephyr: add device tree binding for fan steps
zephyr: add device tree binding for fan steps

Some variant may want use EC control fan steps
with their own algorithm,
introduce fan_steps to zephyr device binding allow variant
create their own fan steps with differnet thermal sensor temperature.

BUG=b:253557900
BRANCH=none
TEST=zmake build -a

Signed-off-by: Zick Wei <3d0b14a1e83601e71d11cd2c38ee93ff1dbbc737@quanta.corp-partner.google.com>
Change-Id: I96dd23b492321113d8b3cda2cb26eb0286e996f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3997772
Reviewed-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Code-Coverage: Zoss <345cf107e82c70959d46f59d98bddc98ce458aff@prod.google.com>
Commit-Queue: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Reviewed-by: Devin Lu <d4ad47e36dbc9c8af8e155263d0bf0afaae16ab2@quantatw.com>
Tested-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Code-Coverage: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec