ARM: dts: da850-evm: enable cpufreq

Enable cpufreq-dt support for da850-evm. The cvdd is supplied by the
tps65070 pmic with configurable output voltage. By default da850-evm
boards support frequencies up to 375MHz so enable this operating
point.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>