Add debug ramdisk variant.

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

This is a reland of f84e9c05e2, with a fix
that removes /first_stage_ramdisk.

Bug: 184004542
Test: soong test
Change-Id: I739de63cfec6b0fec5a90f7c4741fc4d884d209c

sh/sh_binary.go

@@ -210,6 +210,10 @@ func (s *ShBinary) VendorRamdiskVariantNeeded(ctx android.BaseModuleContext) boo
 	return proptools.Bool(s.properties.Vendor_ramdisk_available) || s.ModuleBase.InstallInVendorRamdisk()
 }
 
+func (s *ShBinary) DebugRamdiskVariantNeeded(ctx android.BaseModuleContext) bool {
+	return false
+}
+
 func (s *ShBinary) RecoveryVariantNeeded(ctx android.BaseModuleContext) bool {
 	return proptools.Bool(s.properties.Recovery_available) || s.ModuleBase.InstallInRecovery()
 }