Fix layout for Razer Serval

Ensure all of the keys are mapped.

Test: atest RazerServalTest
Bug: 136263708
Change-Id: I550d5e4e46cbc8549f0bcf075ad5ac39870c3487
diff --git a/data/keyboards/Vendor_1532_Product_0900.kl b/data/keyboards/Vendor_1532_Product_0900.kl
index c2fc1b4..4c6c4dd 100644
--- a/data/keyboards/Vendor_1532_Product_0900.kl
+++ b/data/keyboards/Vendor_1532_Product_0900.kl
@@ -20,13 +20,19 @@
 key 308 BUTTON_Y
 key 310 BUTTON_L1
 key 311 BUTTON_R1
-key 316 BUTTON_MODE
 key 317 BUTTON_THUMBL
 key 318 BUTTON_THUMBR
 
 key 158 BACK
 key 172 HOME
 
+# Left arrow to the left of the "power" key
+key 0x13a BUTTON_SELECT
+# Right arrow to the right of the "power" key
+key 0x13b BUTTON_START
+# Power key
+key 0x13c BUTTON_MODE
+
 axis 0x00 X
 axis 0x01 Y
 axis 0x02 Z