build_rootfs.sh: Add 8250.nr_uarts for rockpi u-boot env am: 31f9aaf0d1 am: cec480c22e

Original change: https://android-review.googlesource.com/c/kernel/tests/+/2004904

Change-Id: I6bf7e38f441e521ad84fadd4183cd93438f03d55
diff --git a/net/test/rootfs/bullseye-rockpi.sh b/net/test/rootfs/bullseye-rockpi.sh
index 6974099..7df36a7 100755
--- a/net/test/rootfs/bullseye-rockpi.sh
+++ b/net/test/rootfs/bullseye-rockpi.sh
@@ -135,7 +135,7 @@
 	gzwrite mmc ${devnum} ${loadaddr} 0x${filesize} 100000 0x1000000
 fi
 load mmc ${devnum}:${distro_bootpart} 0x06080000 /boot/boot.fit
-setenv bootargs "earlycon=uart8250,mmio32,0xff1a0000 console=ttyS2,1500000n8 loglevel=7 sdhci.debug_quirks=0x20000000 root=LABEL=ROOT"
+setenv bootargs "8250.nr_uarts=4 earlycon=uart8250,mmio32,0xff1a0000 console=ttyS2,1500000n8 loglevel=7 sdhci.debug_quirks=0x20000000 root=LABEL=ROOT"
 bootm 0x06080000
 EOF
 mkimage -C none -A arm -T script -d /boot/boot.cmd /boot/boot.scr