bmips: bcm6358: add support for Huawei HG556a ver A

Specifications:
- SoC: Broadcom BCM6358 dual 300MHz MIPS
- Flash: 16MB NOR Spansion S29GL128P10
- RAM: 64MB DDR
- Ethernet: 4x 100M
- Wifi: Atheros AR9223
- 3x USB 2.0 port
- 4x Button
- 13x LED
- RJ11 2x FXS VoIP (unsupported)
- RJ11 xDSL (unsupported)

Install instructions:
- Assign static IP 192.168.1.100 to PC.
- Unplug the power source.
- Press the RESTART button at the router, don't release it yet!
- Plug the power source and wait at least 15 seconds.
- Release the RESTART button.
- Browse to http://192.168.1.1 with your PC.
- Upload the openwrt-bmips-bcm6358-huawei_hg556a-a-squashfs-cfe.bin file.
- Wait some minutes until the firmware upgrade completes.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/bmips/image/bcm6358.mk

@@ -1,5 +1,19 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
+define Device/huawei_hg556a-a
+  $(Device/bcm63xx-cfe-legacy)
+  DEVICE_VENDOR := Huawei
+  DEVICE_MODEL := EchoLife HG556a
+  DEVICE_VARIANT := A
+  CHIP_ID := 6358
+  CFE_BOARD_ID := HW556
+  CFE_EXTRAS += --rsa-signature "EchoLife_HG556a" --tag-version 8
+  IMAGE_OFFSET := 0x20000
+  DEVICE_PACKAGES += $(USB2_PACKAGES) $(ATH9K_PACKAGES) \
+    kmod-leds-gpio
+endef
+TARGET_DEVICES += huawei_hg556a-a
+
 define Device/huawei_hg556a-b
   $(Device/bcm63xx-cfe-legacy)
   DEVICE_VENDOR := Huawei