ARC: [plat-hsdk]: Temporary fix to set CPU frequency to 1GHz

Add temporary fix to HSDK platform code to setup CPU frequency
to 1GHz on early boot.
We can remove this fix when smart hsdk pll driver will be
introduced, see discussion:
https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg02689.html

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>