Add fstab for microdroid & add more kernel commandline params

The vendor_boot.img now has fstab file in it. It currently mounts the
system.img to /system, but eventually we will use the dynamic partitions
in super.img.

A few more essential kernel commandline params are added. Eventually,
these androidboot.* parameters will be given via /proc/bootconfig.

Bug: 178562528
Test: build microdroid-* modules. push microdroid-boot-5.10.img as
boot.img, microdroid-vendor-boot-5.10.img as vendor_boot.img,
micrdroid.img as super.img.
Run assemble_cvd on the device.
Push microdroid-uboot_env.img as uboot_env.img
Run crosvm with the generated composite image. VM goes through the
bootloader, kernel, first stage init, and then second stage init.

Change-Id: Id1ce4f33f912bb80cd280060ecd9cabe57675660
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index dc9a4bb..8ff2b36 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -158,7 +158,28 @@
             deps: ["virt_device_prebuilts_kernel_modules-5.10-x86_64"],
         },
     },
+    deps: [
+        "microdroid_fstab",
+    ],
+    base_dir: "first_stage_ramdisk",
     type: "compressed_cpio",
+    symlinks: [
+        {
+            target: "etc/fstab",
+            name: "first_stage_ramdisk/fstab.microdroid",
+        },
+        {
+            target: "first_stage_ramdisk/lib",
+            name: "lib",
+        },
+    ],
+}
+
+prebuilt_etc {
+    name: "microdroid_fstab",
+    src: "fstab",
+    filename: "fstab",
+    installable: false,
 }
 
 prebuilt_etc {