drm: panel-backlight-quirks: Add Steam Deck brightness quirk

drm: panel-backlight-quirks: Add Steam Deck brightness quirk

On the SteamOS kernel, Valve universally makes minimum brightness 0
for all devices. SteamOS is (was?) meant for the Steam Deck, so
enabling it universally is reasonable. However, it causes issues in
certain devices. Therefore, introduce it just for the Steam Deck here.

SteamOS kernel does not have a public mirror, but this replaces commit
806dd74bb225 ("amd/drm: override backlight min value from 12 -> 0")
in the latest, as of this writing, SteamOS kernel (6.11.11-valve24).
See unofficial mirror reconstructed from sources below.

Link: https://gitlab.com/evlaV/linux-integration/-/commit/806dd74bb225
Reviewed-by: Robert Beckett <bob.beckett@collabora.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
Link: https://lore.kernel.org/r/20250829145541.512671-6-lkml@antheas.dev
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>