pvmfw: use libavb_rs for verification

Use libavb_rs for slot verification. This shouldn't cause any
functionality changes.

Test: atest libpvmfw_avb.integration_test
Change-Id: I06039d91084d392bdbac257702b10fc7e3ade5bb
diff --git a/pvmfw/avb/src/partition.rs b/pvmfw/avb/src/partition.rs
index ca450c9..3fe9479 100644
--- a/pvmfw/avb/src/partition.rs
+++ b/pvmfw/avb/src/partition.rs
@@ -14,8 +14,8 @@
 
 //! Struct and functions relating to well-known partition names.
 
-use crate::utils::is_not_null;
-use core::ffi::{c_char, CStr};
+use avb::IoError;
+use core::ffi::CStr;
 
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 pub(crate) enum PartitionName {
@@ -51,39 +51,28 @@
     }
 }
 
-impl TryFrom<*const c_char> for PartitionName {
-    type Error = avb::IoError;
-
-    fn try_from(partition_name: *const c_char) -> Result<Self, Self::Error> {
-        is_not_null(partition_name)?;
-        // SAFETY: It is safe as the raw pointer `partition_name` is a nonnull pointer.
-        let partition_name = unsafe { CStr::from_ptr(partition_name) };
-        partition_name.try_into()
-    }
-}
-
 impl TryFrom<&CStr> for PartitionName {
-    type Error = avb::IoError;
+    type Error = IoError;
 
     fn try_from(partition_name: &CStr) -> Result<Self, Self::Error> {
         match partition_name.to_bytes_with_nul() {
             Self::KERNEL_PARTITION_NAME => Ok(Self::Kernel),
             Self::INITRD_NORMAL_PARTITION_NAME => Ok(Self::InitrdNormal),
             Self::INITRD_DEBUG_PARTITION_NAME => Ok(Self::InitrdDebug),
-            _ => Err(avb::IoError::NoSuchPartition),
+            _ => Err(IoError::NoSuchPartition),
         }
     }
 }
 
 impl TryFrom<&[u8]> for PartitionName {
-    type Error = avb::IoError;
+    type Error = IoError;
 
     fn try_from(non_null_terminated_name: &[u8]) -> Result<Self, Self::Error> {
         match non_null_terminated_name {
             x if x == Self::Kernel.as_non_null_terminated_bytes() => Ok(Self::Kernel),
             x if x == Self::InitrdNormal.as_non_null_terminated_bytes() => Ok(Self::InitrdNormal),
             x if x == Self::InitrdDebug.as_non_null_terminated_bytes() => Ok(Self::InitrdDebug),
-            _ => Err(avb::IoError::NoSuchPartition),
+            _ => Err(IoError::NoSuchPartition),
         }
     }
 }