crypto: qcom-rng: Make the core clock optional regardless of ACPI presence

Some newer SoCs (like SM8450) do not require a clock vote for the PRNG
to function. Make it entirely optional and rely on the bindings checker
to ensure platforms that need it, consume one.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>