arm64: dts: salvator-x: Add current sense amplifiers

Add device nodes for two Maxim max961x current sense amplifiers
sensing VDD_08 and DVFS_08 lines.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
[geert: r8a7796-salvator-x.dts => salvator-x.dtsi]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>