meta/conf/distro: Make debian inherit DISTRO_APT_SOURCES declaration

To simplify distro introduction move all DISTRO_APT_SOURCES declarations
from debian-*.conf to parent debian-common.conf. Left declaration in
debian-sid-ports.conf untouched because of "-ports" suffix usage.

Signed-off-by: Anton Mikanovich <amikan@ilbers.de>

meta-isar/conf/distro/ubuntu-focal.conf

@@ -5,6 +5,8 @@
 
 require conf/distro/debian-common.conf
 
+BASE_DISTRO = "ubuntu"
+
 DISTRO_APT_SOURCES ?= "conf/distro/${DISTRO}.list"
 DISTRO_APT_SOURCES_arm64 ?= "conf/distro/${DISTRO}-ports.list"
 HOST_DISTRO_APT_SOURCES_append_arm64 = " ${DISTRO_APT_SOURCES}"

meta/conf/distro/debian-bullseye.conf

@@ -6,7 +6,6 @@ BASE_DISTRO_CODENAME = "bullseye"
 
 HOST_DISTRO ?= "debian-${BASE_DISTRO_CODENAME}"
 
-DISTRO_APT_SOURCES ?= "conf/distro/debian-${BASE_DISTRO_CODENAME}.list"
 DISTRO_CONFIG_SCRIPT ?= "debian-configscript.sh"
 DISTRO_KERNELS ?= "4kc-malta 5kc-malta 686 686-pae amd64 arm64 armmp \
     armmp-lpae cloud-amd64 loongson-3 octeon powerpc64le rpi s390x marvell \

meta/conf/distro/debian-buster.conf

@@ -6,7 +6,6 @@ BASE_DISTRO_CODENAME = "buster"
 
 HOST_DISTRO ?= "debian-buster"
 
-DISTRO_APT_SOURCES ?= "conf/distro/debian-buster.list"
 DISTRO_CONFIG_SCRIPT ?= "debian-configscript.sh"
 DISTRO_KERNELS ?= "4kc-malta 5kc-malta 686 686-pae amd64 arm64 armmp \
     armmp-lpae cloud-amd64 loongson-3 marvell octeon powerpc64le rpi s390x \

meta/conf/distro/debian-common.conf

@@ -6,6 +6,7 @@
 BASE_DISTRO = "debian"
 
 HOST_DISTRO_APT_SOURCES ?= "conf/distro/${HOST_DISTRO}.list"
+DISTRO_APT_SOURCES ?= "conf/distro/${BASE_DISTRO}-${BASE_DISTRO_CODENAME}.list"
 
 WIC_IMAGER_INSTALL = "parted \
                       gdisk \

meta/conf/distro/debian-stretch.conf

@@ -7,7 +7,6 @@ BASE_DISTRO_CODENAME = "stretch"
 
 HOST_DISTRO ?= "debian-stretch"
 
-DISTRO_APT_SOURCES ?= "conf/distro/debian-stretch.list"
 DISTRO_CONFIG_SCRIPT ?= "debian-configscript.sh"
 DISTRO_KERNELS ?= "4kc-malta 586 5kc-malta 686 686-pae amd64 arm64 armmp \
     armmp-lpae kirkwood loongson-3 marvell octeon orion5x powerpc64le \