configs: nx25-ae250:Rename as ax25-ae350

Rename
 nx25 as ax25
 ae250 as ae350
 nx25-ae250 as ax25-ae350
 including filename, variable, string and definition.

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Cc: Greentime Hu <green.hu@gmail.com>

configs/ax25-ae350_defconfig

@@ -1,7 +1,7 @@
 CONFIG_RISCV=y
 CONFIG_SYS_TEXT_BASE=0x00000000
-CONFIG_DEFAULT_DEVICE_TREE="ae250"
-CONFIG_TARGET_NX25_AE250=y
+CONFIG_DEFAULT_DEVICE_TREE="ae350"
+CONFIG_TARGET_AX25_AE350=y
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
 # CONFIG_AUTO_COMPLETE is not set