ARC: [plat-hsdk]: Set initial core pll output frequency

Set initial core pll output frequency specified in device tree to
1GHz. It will be applied at the core pll driver probing.

Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>