dt-bindings: arm: samsung: Update the CHIPID binding for ASV

This patch adds documentation of new optional "samsung,asv-bin"
property in the chipid device node and documents requirement of
"syscon" compatible string.  These additions are needed to support
Exynos ASV (Adaptive Supply Voltage) feature.

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
[robh: drop 'select' which is no longer needed. Fix up example whitespace]
Signed-off-by: Rob Herring <robh@kernel.org>