Add 'vendor.' prefix to a vendor HAL service name

To prevent property name collisions between properties of system and
vendor, 'vendor.' prefix must be added to a vendor HAL service name.
You can see the details in http://go/treble-sysprop-compatibility.

Test: succeeded building and tested on a walleye device
Bug: 36796459
Change-Id: I4e8fbee791ec917a8f627a1366f4d44ec7e6febc
diff --git a/graphics/composer/2.1/default/android.hardware.graphics.composer@2.1-service.rc b/graphics/composer/2.1/default/android.hardware.graphics.composer@2.1-service.rc
index 51b0e3b..3b6710b 100644
--- a/graphics/composer/2.1/default/android.hardware.graphics.composer@2.1-service.rc
+++ b/graphics/composer/2.1/default/android.hardware.graphics.composer@2.1-service.rc
@@ -1,4 +1,4 @@
-service hwcomposer-2-1 /vendor/bin/hw/android.hardware.graphics.composer@2.1-service
+service vendor.hwcomposer-2-1 /vendor/bin/hw/android.hardware.graphics.composer@2.1-service
     class hal animation
     user system
     group graphics drmrpc