arm64: dts: rockchip: Add maskrom button to Radxa E20C

arm64: dts: rockchip: Add maskrom button to Radxa E20C

Radxa E20C has two buttons, one SARADC maskrom button and one GPIO user
button.

Add support for the maskrom button using a adc-keys node, also add the
regulators used by SARADC controller.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Link: https://lore.kernel.org/r/20250304201642.831218-5-jonas@kwiboo.se
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
[ upstream commit: 3a2819ee9c71d1c6388e456cc4eb042914d15d7e ]

(cherry picked from commit 460ef5b623e5fa69843305faf50f6b1a8e81e1cd)
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>