Use TARGET_SCREEN_DENSITY

This variable is used to auto-populate the ro.sf.lcd_density as
well as selecting density bucket for resources in recovery.
diff --git a/axolotl/BoardConfig.mk b/axolotl/BoardConfig.mk
index dfc04e1..7cea376 100644
--- a/axolotl/BoardConfig.mk
+++ b/axolotl/BoardConfig.mk
@@ -3,6 +3,7 @@
 # Board Information
 TARGET_BOOTLOADER_BOARD_NAME := axolotl
 TARGET_BOARD_PLATFORM := axolotl
+TARGET_SCREEN_DENSITY := 400
 
 # Kernel/boot.img Configuration
 BOARD_KERNEL_CMDLINE += androidboot.hardware=axolotl