ARM: meson: rework soc arch file to prepare for new SoC

We are about to add support for the Amlogic AXG SoC. While very close to
the Gx SoC family, we will need to handle a few thing which are different
in this SoC. Rework the meson arch directory to prepare for this.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/arch/arm/mach-meson/Makefile b/arch/arm/mach-meson/Makefile
index 8ad9b3e..78345b4 100644
--- a/arch/arm/mach-meson/Makefile
+++ b/arch/arm/mach-meson/Makefile
@@ -2,4 +2,5 @@
 #
 # Copyright (c) 2016 Beniamino Galvani <b.galvani@gmail.com>
 
-obj-y += board.o sm.o eth.o
+obj-y += board-common.o sm.o
+obj-$(CONFIG_MESON_GX) += board-gx.o