memory: tegra20-emc: Add runtime dependency on devfreq governor module

memory: tegra20-emc: Add runtime dependency on devfreq governor module

Tegra20 EMC driver uses simple devfreq governor. Add simple devfreq
governor to the list of the Tegra20 EMC driver module softdeps to allow
userspace initramfs tools like dracut to automatically pull the devfreq
module into ramfs image together with the EMC module.

Reported-by: Nicolas Chauvet <kwizart@gmail.com>
Suggested-by: Nicolas Chauvet <kwizart@gmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20211019231524.888-1-digetx@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>