build_rootfs.sh: Add 8250.nr_uarts=X am: db23c1a5bd am: 35af13dacb

Original change: https://android-review.googlesource.com/c/kernel/tests/+/2004333

Change-Id: I0d8414ca726179adc36f7b4833ae2c247efa23a4
tree: 17f8849a6de827449e1c5f4b62caf67bec3424aa
  1. devicetree/
  2. net/
  3. Android.bp
  4. METADATA