dt-bindings: mediatek: Add binding for MT6779 SMI

This patch add description for MT6779 SMI.
There are GALS in smi-larb but without clock of GALS alone.

changelog since v2:
Add GALS for mt6779 in smi-common.txt

Signed-off-by: Ming-Fan Chen <ming-fan.chen@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1578465691-30692-3-git-send-email-ming-fan.chen@mediatek.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>