boards: siemens: iot2050: Unify PG1 and PG2/M.2 configurations again

This avoids having to maintain to defconfigs that are 99% equivalent.
The approach is to use binman to generate two flash images,
flash-pg1.bin and flash-pg2.bin. With the help of a template dtsi, we
can avoid duplicating the common binman image definitions.

Suggested-by: Andrew Davis <afd@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/board/siemens/iot2050/MAINTAINERS b/board/siemens/iot2050/MAINTAINERS
index aa21de2..1b52535 100644
--- a/board/siemens/iot2050/MAINTAINERS
+++ b/board/siemens/iot2050/MAINTAINERS
@@ -4,7 +4,6 @@
 S:	Maintained
 F:	board/siemens/iot2050/
 F:	include/configs/iot2050.h
-F:	configs/iot2050_pg1_defconfig
-F:	configs/iot2050_pg2_defconfig
+F:	configs/iot2050_defconfig
 F:	arch/arm/dts/iot2050-*
 F:	doc/board/siemens/iot2050.rst