DRM: AIDL HAL may replace HIDL HAL

Relax the requirement on compatibility matrices
that HIDL DRM HAL must exist on devices with
target level 3~6, because they may have the AIDL
DRM HAL instead.

Issue: FP3-A13#292
Change-Id: Ia45931e398aa056a5d9695f50e0b689afb1a2190
(cherry picked from commit 20231e082a8c6df0affced33733f0148d57297cb)
diff --git a/compatibility_matrices/compatibility_matrix.3.xml b/compatibility_matrices/compatibility_matrix.3.xml
index 0964c99..bca0b37 100644
--- a/compatibility_matrices/compatibility_matrix.3.xml
+++ b/compatibility_matrices/compatibility_matrix.3.xml
@@ -147,7 +147,7 @@
             <regex-instance>.*</regex-instance>
         </interface>
     </hal>
-    <hal format="hidl" optional="false">
+    <hal format="hidl" optional="true">
         <name>android.hardware.drm</name>
         <version>1.1</version>
         <interface>