Increase ARM64 memory for microdroid test

--mem 125 is too low, and it makes MicrodroidHostTestCases fail on arm64
devices.

Test: atest MicrodroidHostTestCases
Change-Id: Ie5f77ced45125bcab6df4e1531ca13ec5884f089
diff --git a/tests/hostside/java/android/virt/test/MicrodroidTestCase.java b/tests/hostside/java/android/virt/test/MicrodroidTestCase.java
index 3f80cdf..c2ef566 100644
--- a/tests/hostside/java/android/virt/test/MicrodroidTestCase.java
+++ b/tests/hostside/java/android/virt/test/MicrodroidTestCase.java
@@ -34,7 +34,7 @@
     private static final String APK_NAME = "MicrodroidTestApp.apk";
     private static final String PACKAGE_NAME = "com.android.microdroid.test";
 
-    private static final int MIN_MEM_ARM64 = 125;
+    private static final int MIN_MEM_ARM64 = 256;
     private static final int MIN_MEM_X86_64 = 400;
 
     private int minMemorySize() throws DeviceNotAvailableException {