siemens: Move CONFIG_FACTORYSET to Kconfig

Introduce board/siemens/common/Kconfig and have it hold FACTORYSET to
start with.  Use select for this on the boards that need it.

Cc: Anatolij Gustschin <agust@denx.de>
Cc: Samuel Egli <samuel.egli@siemens.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-imx/imx8/Kconfig b/arch/arm/mach-imx/imx8/Kconfig
index 5e1b20a..8f185c1 100644
--- a/arch/arm/mach-imx/imx8/Kconfig
+++ b/arch/arm/mach-imx/imx8/Kconfig
@@ -57,11 +57,13 @@
 config TARGET_DENEB
 	bool "Support i.MX8QXP Capricorn Deneb board"
 	select BOARD_LATE_INIT
+	select FACTORYSET
 	select IMX8QXP
 
 config TARGET_GIEDI
 	bool "Support i.MX8QXP Capricorn Giedi board"
 	select BOARD_LATE_INIT
+	select FACTORYSET
 	select IMX8QXP
 
 config TARGET_IMX8QM_MEK