arm64: dts: apq8096-db820c: Enable on board 3 pcie root complex

This patch adds enables 3 instances of root complexes which are
exposed on DB820c board. 3 Instances are terminted as below
PCIE0 => QCA6174
PCIE1 => MINI PCIE CARD
PCIE2 => GBE ETHERNET

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>