armTrustedFirmware: Fix bintools 2.39 regression (LOAD segment with RWX)

Fixes:

```
.../aarch64-unknown-linux-gnu-ld.bfd: warning: /build/source/build/rk3399/release/bl31/bl31.elf has a LOAD segment with RWX permissions
.../aarch64-unknown-linux-gnu-ld.bfd: warning: /build/source/build/rk3399/release/bl31/bl31.elf has a LOAD segment with RWX permissions
.../aarch64-unknown-linux-gnu-ld.bfd: warning: /build/source/build/rk3399/release/bl31/bl31.elf has a LOAD segment with RWX permissions
make: *** [Makefile:1306: /build/source/build/rk3399/release/bl31/bl31.elf] Error 1
```

See: https://developer.trustedfirmware.org/T996

pkgs/misc/arm-trusted-firmware/default.nix

@@ -53,6 +53,10 @@ let
 
     makeFlags = [
       "CROSS_COMPILE=${stdenv.cc.targetPrefix}"
+      # binutils 2.39 regression
+      # `warning: /build/source/build/rk3399/release/bl31/bl31.elf has a LOAD segment with RWX permissions`
+      # See also: https://developer.trustedfirmware.org/T996
+      "LDFLAGS=-no-warn-rwx-segments"
     ] ++ (lib.optional (platform != null) "PLAT=${platform}")
       ++ extraMakeFlags;