Disable ramdump with debug policy

This CL disables ramdump if debug policy doesn't explicitly
enables ramdump via ramdump prop in the /avf/guest/common node.

The virtualization service always provides crashkernel=17M via
kernel command, so this CL removes crashkernel=17MB in the
microdroid's bootargs in the /chosen node.

Here's the test result on my machine with MicrodroidTestApp.

  - Before the CL (or this CL + ramdump is enabled)
    $ adb shell /proc/meminfo
    MemTotal:         212968 kB
    MemFree:          138336 kB
    MemAvailable:     171980 kB

  - With this CL + ramdump is disabled
    $ adb shell /proc/meminfo
    MemTotal:         230372 kB
    MemFree:          165240 kB
    MemAvailable:     192648 kB

Bug: 243630590
Test:  Boot microdroid with following AVF debug policies \
  - AVF debug policy exists, and ramdump=<1> \
  - AVF debug policy exists, and ramdump=<0> \
  - No AVF debug policy
Change-Id: Ia486448b5513c2d5662a4f16ddb3334b20913329
diff --git a/libs/libfdt/src/lib.rs b/libs/libfdt/src/lib.rs
index 8fd1879..29d7abe 100644
--- a/libs/libfdt/src/lib.rs
+++ b/libs/libfdt/src/lib.rs
@@ -388,6 +388,23 @@
         fdt_err_expect_zero(ret)
     }
 
+    /// Create or change a property name-value pair to the given node.
+    pub fn setprop(&mut self, name: &CStr, value: &[u8]) -> Result<()> {
+        // SAFETY - New value size is constrained to the DT totalsize
+        //          (validated by underlying libfdt).
+        let ret = unsafe {
+            libfdt_bindgen::fdt_setprop(
+                self.fdt.as_mut_ptr(),
+                self.offset,
+                name.as_ptr(),
+                value.as_ptr().cast::<c_void>(),
+                value.len().try_into().map_err(|_| FdtError::BadValue)?,
+            )
+        };
+
+        fdt_err_expect_zero(ret)
+    }
+
     /// Get reference to the containing device tree.
     pub fn fdt(&mut self) -> &mut Fdt {
         self.fdt