dt-bindings: rng: Add Marvell Armada RNG support

The Marvell Armada RNG uses the same IP as TI from Inside Secure and is
already using the binding. The only missing part is the
"marvell,armada-8k-rng" compatible string.

Rename the binding to inside-secure,safexcel-eip76.yaml to better
reflect it is multi-vendor, licensed IP and to follow the naming
convention using compatible string.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>