ipq40xx: add support for MikroTik SXTsq 5 ac

This commit adds support for the MikroTik SXTsq 5 ac (RBSXTsqG-5acD),
an outdoor 802.11ac wireless CPE with one 10/100/1000 Mbps Ethernet
port.

Specifications:
 - SoC: Qualcomm Atheros IPQ4018
 - RAM: 256 MB
 - Storage: 16 MB NOR
 - Wireless: IPQ4018 (SoC) 802.11a/n/ac 2x2:2, 16 dBi antennae
 - Ethernet: IPQ4018 (SoC) 1x 10/100/1000 port, 10-28 Vdc PoE in
 - 1x Ethernet LED (green)
 - 7x user-controllable LEDs
  · 1x power (blue)
  · 1x user (green)
  · 5x rssi (green)

Note:
 Serial UART is probably available on the board, but it has not been
 tested.

Flashing:
 Boot via TFTP the initramfs image. Then, upload a sysupgrade image
 via SSH and flash it normally. More info at the "Common procedures
 for MikroTik products" page https://openwrt.org/toh/mikrotik/common.

Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
(cherry picked from commit d1f1e5269e)
[Compile and Run Tested]
Signed-off-by: Nick Hainke <vincent@systemli.org>

target/linux/ipq40xx/patches-5.4/901-arm-boot-add-dts-files.patch

@@ -10,7 +10,7 @@ Signed-off-by: John Crispin <john@phrozen.org>
 
 --- a/arch/arm/boot/dts/Makefile
 +++ b/arch/arm/boot/dts/Makefile
-@@ -837,11 +837,59 @@ dtb-$(CONFIG_ARCH_QCOM) += \
+@@ -837,11 +837,60 @@ dtb-$(CONFIG_ARCH_QCOM) += \
  	qcom-apq8074-dragonboard.dtb \
  	qcom-apq8084-ifc6540.dtb \
  	qcom-apq8084-mtp.dtb \
@@ -32,6 +32,7 @@ Signed-off-by: John Crispin <john@phrozen.org>
 +	qcom-ipq4018-jalapeno.dtb \
 +	qcom-ipq4018-meshpoint-one.dtb \
 +	qcom-ipq4018-hap-ac2.dtb \
++	qcom-ipq4018-sxtsq-5-ac.dtb \
 +	qcom-ipq4018-nbg6617.dtb \
 +	qcom-ipq4019-oap100.dtb \
 +	qcom-ipq4018-pa1200.dtb \