Add support for Xiaomi Redmi Ax5400 (white version)

[raenye]

Some ipq5018 progress is reported here:

IPQ5018: Potential future support for Linksys MX2000 Atlas 6 & MX5500 Atlas 6 Pro

hi all, Got my hands on a Linksys Atlas 6 MX2000 and connected it to serial. Pinout: GND -empty- RX - TX -empty (starting from GND label) [MX2000 pinout] While upstream kernel support for IPQ5018 is being worked on, I thought I pasted the output of the bootlog and other info below for potential support in the future: bootlog: Format: Log Type - Time(microsec) - Message - Optional Info Log Type: B - Since Boot(Power On Reset), D - Delta, S - Statistic S - QC_IMAGE_VERSION_STRING=BOOT.BF.…