Build kdump only for 64-bit

It doesn't support 32-bit target. Build crashdump, kexec, and the kernel
only for 64-bit and disable the 32-bit variant.

Bug: N/A
Test: build for aosp_x86 and full
Change-Id: I3fafff4a1a45ab808aa3b8cd720925c6b8f4fef3
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index 6e9a6de..3bbab13 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -90,9 +90,6 @@
         "microdroid_property_contexts",
         "microdroid_service_contexts",
 
-        "microdroid_kexec",
-        "microdroid_crashdump_kernel",
-
         // TODO(b/195425111) these should be added automatically
         "libcrypto", // used by many (init_second_stage, microdroid_manager, toybox, etc)
         "liblzma", // used by init_second_stage
@@ -113,6 +110,8 @@
                 "apkdmverity",
                 "authfs",
                 "authfs_service",
+                "microdroid_crashdump_kernel",
+                "microdroid_kexec",
                 "microdroid_manager",
                 "zipfuse",
             ],