This patch adds DTS entries for Designware I2C controllers used in
APM X-Gene v2 evaluation platform (Merlin board).

X-Gene v2 has total 5 I2C controllers. On Merlin board only I2C1
and I2C4 controllers are available in Linux, where the other 3
controllers are used for management purpose (power management,
BMC function).
Signed-off-by: Duc Dang <dhdang@apm.com>