ARC: [plat-hsdk]: Get rid of core pll frequency set in platform code

Get rid of core pll frequency set in platform code as we set it via
device tree using 'assigned-clock-rates' property.

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