add userinit script(s) support

Allow user to provide userinit.sh and/or userinit.d/*
scripts under /data/local to be run on each boot.

Change-Id: I96f3034bcdea8d4cc75929d21b69efa31c1cb108
diff --git a/config/common.mk b/config/common.mk
index 5438091..bd1f392 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -40,6 +40,10 @@
     vendor/cm/prebuilt/common/etc/init.d/00banner:system/etc/init.d/00banner \
     vendor/cm/prebuilt/common/bin/sysinit:system/bin/sysinit
 
+# userinit support
+PRODUCT_COPY_FILES += \
+    vendor/cm/prebuilt/common/etc/init.d/90userinit:system/etc/init.d/90userinit
+
 # Compcache/Zram support
 PRODUCT_COPY_FILES += \
     vendor/cm/prebuilt/common/etc/init.local.rc:system/etc/init.local.rc \