ipqx0xx: add Generic subtarget

Both targets miss a subtarget causing an image naming style which is
different from other all othe targets, even tho it already uses
`x/generic/` as subfolder as if the subtarget would exist.

This commit adds the Generic subtarget resulting in consistent naming.

    ~/src/openwrt/openwrt/bin/targets/ipq806x/generic$ ls
    openwrt-ipq806x-generic-netgear_d7800-initramfs-uImage
    openwrt-ipq806x-generic-netgear-d7800.manifest
    openwrt-ipq806x-generic-netgear_d7800-squashfs-factory.img
    openwrt-ipq806x-generic-netgear_d7800-squashfs-sysupgrade.bin

CC: John Crispin <john@phrozen.org>

Signed-off-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit 853e4dd306)

target/linux/ipq40xx/Makefile

@@ -7,6 +7,7 @@ FEATURES:=squashfs fpu ramdisk nand
 CPU_TYPE:=cortex-a7
 CPU_SUBTYPE:=neon-vfpv4
 MAINTAINER:=John Crispin <john@phrozen.org>
+SUBTARGETS:=generic
 
 # TODO: drop kmod-usb-dwc3-of-simple when migrating to 4.19
 KERNEL_PATCHVER:=4.14

target/linux/ipq40xx/generic/target.mk

@@ -0,0 +1 @@
+BOARDNAME:=Generic

target/linux/ipq806x/Makefile

@@ -9,6 +9,7 @@ FEATURES:=squashfs nand fpu ramdisk
 CPU_TYPE:=cortex-a15
 CPU_SUBTYPE:=neon-vfpv4
 MAINTAINER:=John Crispin <john@phrozen.org>
+SUBTARGETS:=generic
 
 KERNEL_PATCHVER:=4.14
 

target/linux/ipq806x/generic/target.mk

@@ -0,0 +1 @@
+BOARDNAME:=Generic