vmbase_example: Clarify that the payload is a BIOS

Rename all Soong targets to include "_bios" and refactor the linker
script and idmap.S to be preprocessed and receive a CPP macro
representing the "mode". Rename image.ld to reflect this.

Modify the test to use the new "_bios" binary name and refactor it to
make the core logic re-usable for future vmbase_example modes.

No functional change intended.

Test: atest vmbase_example.integration_test
Change-Id: I06679d154494d85916ff534298a066519b1b0778
diff --git a/tests/vmbase_example/Android.bp b/tests/vmbase_example/Android.bp
index 6e902b1..d652196 100644
--- a/tests/vmbase_example/Android.bp
+++ b/tests/vmbase_example/Android.bp
@@ -18,7 +18,7 @@
         "libvmclient",
     ],
     data: [
-        ":vmbase_example_bin",
+        ":vmbase_example_bios_bin",
     ],
     test_suites: ["general-tests"],
     enabled: false,