ARM: mvebu: add SAR frequency values for 1.8/2.0GHz

The Armada-38x has 1.8GHz and 2.0GHz variants. Add entries for these
variants to the sar_freq_tab.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>