raviole: Pull init.insmod.*.cfg from vendor_dlkm

We've started pushing init.insmod.*.cfg into the kernel prebuilts, and
installing it to /vendor_dlkm/etc, but it may not be available on all
prebuilt variants (e.g., kernel 5.10).

Here, we:
1. conditionally install our common init.*cfg to /vendor_dlkm (only if
   $(TARGET_KERNEL_DIR) doesn't have a copy)
2. point init at /vendor_dlkm/etc

When we've cycled completely off of kernel 5.10, we can drop #1.

Bug: 369686096
Test: build, boot
Flag: EXEMPT refactor
Change-Id: Ibefafbcfe1fdf9b4e65ee3d73126c33f04ee193b
diff --git a/conf/init.slider.rc b/conf/init.slider.rc
index 49c20ea..db78b71 100644
--- a/conf/init.slider.rc
+++ b/conf/init.slider.rc
@@ -16,7 +16,7 @@
     start insmod_sh_slider
 
 
-service insmod_sh_slider /vendor/bin/insmod.sh /vendor/etc/init.insmod.slider.cfg
+service insmod_sh_slider /vendor/bin/insmod.sh /vendor_dlkm/etc/init.insmod.slider.cfg
     class main
     user root
     group root system