arm64: dts: add APM Merlin Board device tree

This patch adds the support for APM Merlin board. The Merlin board
is based on the APM X-Gene Shadowcat SoC. This DTS enables PMU,
Ethernet, SATA and Serial.

[dhdang: remove pcie0 node]
Signed-off-by: Feng Kan <fkan@apm.com>
Signed-off-by: Duc Dang <dhdang@apm.com>