ARM: dts: Add initial support for Mediatek mt6582

Add initial support for Mediatek mt6582 and Prestigio
PMT5008 3G tablet, 4 uart, wdt work, init loads successfully. SMP doesn't
work.

Signed-off-by: Maxim Kutnij <gtk3@inbox.ru>
Link: https://lore.kernel.org/r/20211219183134.3849-1-gtk3@inbox.ru


[mb: fix commit subject line]
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>