The Marvell Berlin BG2CD has 3 watchdogs which are compatible with the
snps,dw-wdt driver sit in the sysmgr domain. This patch adds the
corresponding device tree nodes.

NOTE: although BG2CD doesn't have a HW sysmgr, but the sysmgr domain
exists.
Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>