airoha: Clarify subtarget compatibility

Clarify compatibility of the two subtargets with different SoCs to
reduce confusion. The added SoC names only differ in small details such
as features enabled (PoN vs DSL for example).

Signed-off-by: Andreas Gnau <andreas.gnau@iopsys.eu>
Link: https://github.com/openwrt/openwrt/pull/16785
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

target/linux/airoha/an7581/target.mk

@@ -1,6 +1,6 @@
 ARCH:=aarch64
 SUBTARGET:=an7581
-BOARDNAME:=AN7581
+BOARDNAME:=AN7581 / AN7566 / AN7551
 CPU_TYPE:=cortex-a53
 KERNELNAME:=Image dtbs
 FEATURES+=pwm source-only

target/linux/airoha/en7523/target.mk

@@ -1,6 +1,6 @@
 ARCH:=arm
 SUBTARGET:=en7523
-BOARDNAME:=EN7523
+BOARDNAME:=EN7523 / EN7529 / EN7562
 CPU_TYPE:=cortex-a7
 KERNELNAME:=Image dtbs
-FEATURES+=source-only
+FEATURES+=source-only