ipq40xx: add support for P&W R619AC (aka G-DOCK 2.0)

ipq40xx: add support for P&W R619AC (aka G-DOCK 2.0)

P&W R619AC is a IPQ4019 Dual-Band AC1200 router.
It is made by P&W (p2w-tech.com) known as P&W R619AC
but marketed and sold more popularly as G-DOCK 2.0.

Specification:

* SOC: Qualcomm Atheros IPQ4019 (717 MHz)
* RAM: 512 MiB
* Flash: 16 MiB (NOR) + 128 MiB (NAND)
* Ethernet: 5 x 10/100/1000 (4 x LAN, 1 x WAN)
* Wireless:
  - 2.4 GHz b/g/n Qualcomm Atheros IPQ4019
  - 5 GHz a/n/ac Qualcomm Atheros IPQ4019
* USB: 1 x USB 3.0
* LED: 4 x LAN, 1 x WAN, 2 x WiFi, 1 x Power (All Blue LED)
* Input: 1 x reset
* 1 x MicroSD card slot
* Serial console: 115200bps, pinheader J2 on PCB
* Power: DC 12V 2A
* 1 x Unpopulated mPCIe Slot (see below how to connect it)
* 1 x Unpopulated Sim Card Slot

Installation:
1. Access to tty console via UART serial
2. Enter failsafe mode and mount rootfs
   <https://openwrt.org/docs/guide-user/troubleshooting/failsafe_and_factory_reset>
3. Edit inittab to enable shell on tty console
   `sed -i 's/#ttyM/ttyM/' /etc/inittab`
4. Reboot and upload `-nand-factory.bin` to the router (using wget)
5. Use `sysupgrade` command to install

Another installation method is to hijack the upgrade server domain
of stock firmware, because it's using insecure http.

This commit is based on @LGA1150(at GitHub)'s work
<https://github.com/LGA1150/openwrt/commit/a4932c8d5a275d1fb4297bd20ec03f9270a45d1c>
With some changes:
1. Added `qpic_bam` node in dts. I don't know much about this,
   but I observed other dtses have this node.
2. Removed `ldo` node under `sd_0_pinmux`, because `ldo` cause SD card not
   working. This fix is from
   <https://github.com/coolsnowwolf/lede/commit/51143b4c7571f717afe071db60bbb4db1532cbf2>
3. Removed the 32MB NOR variant.
4. Removed `cd-gpios` in `sdhci` node, because it's reported that it makes
   wlan2g led light up.
5. Added ethphy led config in dts.
6. Changed nand partition label from `rootfs` to `ubi`.

About the 128MiB variant: The stock bootloader sets size of nand to 64MiB.
But most of this devices have 128MiB nand. If you want to use all 128MiB,
you need to modify the `MIBIB` data of bootloader. More details can be
found on github:
<https://github.com/openwrt/openwrt/pull/3691#issuecomment-818770060>
For instructions on how to flash the MIBIB partition from u-boot console:
<https://github.com/openwrt/openwrt/pull/3691#issuecomment-819138232>

About the Mini PCIe slot: (from "ygleg")
"The REFCLK signals on the Mini PCIe slot is not connected on
this board out of the box. If you want to use the Mini PCIe slot
on the board, you need to (preferably) solder two 0402 resistors:
R436 (REFCLK+) and R444 (REFCLK-)..."
This and much more information is provoided in the github comment:
<https://github.com/openwrt/openwrt/pull/3691#issuecomment-968054670>

Signed-off-by: Richard Yu <yurichard3839@gmail.com>
Signed-off-by: DENG Qingfang <dqfext@gmail.com>
[Added comment about MIBIB+128 MiB variant. Added commit
message section about pcie slot. Renamed gpio-leds' subnodes
and added color, function+enum properties.]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>