updater: Add support for FKM OTA kernel updates

Link for users:
https://raw.githubusercontent.com/Zile995/android_kernel_xiaomi_msm8953/oreo-mr1/updater/update.json

Signed-off-by: Zile995 <stefan.zivkovic995@gmail.com>

Author: Zile995

updater/changelog

@@ -0,0 +1,13 @@
+**Kernel: Underground Kernel**
+
+Device: Redmi Note 4(X) Snapdragon (mido)
+Compiler: AOSP Clang 10.0.1
+
+- Latest Linux kernel updates from android-3.18 common tree (synced with sources up to January 15, 2020).
+- Reverted one problematic commit from android common tree.
+- Optimized thermal zones again, less heating/a little safer configuration
+- Anykernel3 updates.
+- Added support for FKM OTA kernel updates.
+  - Do not use FKM OTA updates over the other custom kernels!
+  - You can use it with stock or Underground kernel only!
+- Kernel works on Oreo and Pie only.

updater/update.json

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+{
+  "kernel": {
+    "name": "Underground Kernel",
+    "version": "r43",
+    "link": "https://github.com/Zile995/android_kernel_xiaomi_msm8953/releases/download/r43/UndergroundKernel-mido-20200115.zip",
+    "changelog_url": "https://raw.githubusercontent.com/Zile995/android_kernel_xiaomi_msm8953/oreo-mr1/updater/changelog",
+    "date": "2020-01-15",
+    "sha1": "3685fa5d50f61ed742acd8787dbaf9f851c29cf5"
+  },
+  "support": {
+    "link": "https://t.me/rn4official"
+  }
+}
+