FYI (I know this is an old thread but I can't leave it un-answered),
the DJI P1 is indeed a custom DJI SoC. It's basically a "clone" of the LC1860 DSP architecture (2x CEVA XC4500 + 1x CEVA-X1643), with two independent Cortex-A7 CPUs, one running the RF stack and one running Linux, with added video capture, encoding, decoding and output capabilities.
root@pigeon_wm150_tiny:/ # uname -a
Linux localhost 4.9.130-645274-g4a83e11 #1 SMP PREEMPT Tue Jun 23 04:23:20 CST 2020 armv7l
root@pigeon_wm150_tiny:/ # cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 8.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5
Hardware : PIGEON
Revision : 0000
Serial : 0000000000000000
Bootlog (dmesg) attached.