machine: Clean-up of i.MX8MM machine

Also small changes to the Kernel include file.

(cherry picked from commit 49cec441)

conf/machine/imx8mguf.conf

 #@TYPE: Machine
 #@NAME: SECO North i.MX8M Mini
 #@SOC: i.MX8M Mini
-#@DESCRIPTION: Machine configuration for SECO North i.MX8MM platforms
+#@DESCRIPTION: Machine configuration for SECO Northern Europe i.MX8MM platforms
 
 require include/imx8guf.inc
 

recipes-kernel/linux/linux-seconorth.inc

@@ -4,11 +4,11 @@ SECTION = "kernel"
 LICENSE = "GPL-2.0-only"
 LIC_FILES_CHKSUM ?= "file://COPYING;md5=6bc538ed5bd9a7fc9398086aedcd7e46"
 
-inherit kernel
+inherit kernel kernel-devicetree
 
 DEPENDS += " openssl-native util-linux-native lzop-native "
 
-EXTRA_OEMAKE += " 'DTC_FLAGS=-@' "
+KERNEL_DTC_FLAGS += " -@ "
 
 # Remove ${PKGE}- from file names, as PE is always unset,
 # it generates the -- in the name