Modify prebuilt_kernel_modules behave more like `build-image-kernel-modules-depmod`

This change defines a depmod staging directory for vendor_ramdisk
partition prebuilt kernel modules, and also modifies the build commands
of `modules.dep` to add the leading slash for vendor ramdisk kernel
modules.

Test: unpack and diff soong and make generated vendor ramdisk partitions
Bug: 381104942
Change-Id: I0d14ed676983976e20c7aca98b1c06ce097b1682
diff --git a/kernel/prebuilt_kernel_modules.go b/kernel/prebuilt_kernel_modules.go
index ec7a971..1225da0 100644
--- a/kernel/prebuilt_kernel_modules.go
+++ b/kernel/prebuilt_kernel_modules.go
@@ -247,6 +247,8 @@
 		return modulesDir.Join(ctx, "vendor", "lib", "modules")
 	} else if ctx.InstallInOdmDlkm() {
 		return modulesDir.Join(ctx, "odm", "lib", "modules")
+	} else if ctx.InstallInVendorRamdisk() {
+		return modulesDir.Join(ctx, "lib", "modules")
 	} else {
 		// not an android dlkm module.
 		return modulesDir
@@ -309,8 +311,8 @@
 	builder.Build("depmod", fmt.Sprintf("depmod %s", ctx.ModuleName()))
 
 	finalModulesDep := modulesDep
-	// Add a leading slash to paths in modules.dep of android dlkm
-	if ctx.InstallInSystemDlkm() || ctx.InstallInVendorDlkm() || ctx.InstallInOdmDlkm() {
+	// Add a leading slash to paths in modules.dep of android dlkm and vendor ramdisk
+	if ctx.InstallInSystemDlkm() || ctx.InstallInVendorDlkm() || ctx.InstallInOdmDlkm() || ctx.InstallInVendorRamdisk() {
 		finalModulesDep = modulesDep.ReplaceExtension(ctx, "intermediates")
 		ctx.Build(pctx, android.BuildParams{
 			Rule:   addLeadingSlashToPaths,