Add debug ramdisk variant.

A module will be installed to /debug_ramdisk if debug_ramdisk is set to
true.

This is a reland of f84e9c05e2103149162e4a78a68f20c164fbbba2, with a fix
that removes /first_stage_ramdisk.

Bug: 184004542
Test: soong test
Change-Id: I739de63cfec6b0fec5a90f7c4741fc4d884d209c
diff --git a/android/arch.go b/android/arch.go
index d7b12bc..a63d630 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -665,7 +665,7 @@
 	}
 
 	// only the primary arch in the ramdisk / vendor_ramdisk / recovery partition
-	if os == Android && (module.InstallInRecovery() || module.InstallInRamdisk() || module.InstallInVendorRamdisk()) {
+	if os == Android && (module.InstallInRecovery() || module.InstallInRamdisk() || module.InstallInVendorRamdisk() || module.InstallInDebugRamdisk()) {
 		osTargets = []Target{osTargets[0]}
 	}