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/beryllium/BoardConfig.mk b/beryllium/BoardConfig.mk
index 3e1d727..4d14d8a 100644
--- a/beryllium/BoardConfig.mk
+++ b/beryllium/BoardConfig.mk
@@ -4,6 +4,7 @@
 # Board Information
 TARGET_BOOTLOADER_BOARD_NAME := beryllium
 TARGET_BOARD_PLATFORM := beryllium
+TARGET_SCREEN_DENSITY := 400
 
 # Kernel/boot.img Configuration
 BOARD_KERNEL_CMDLINE     += androidboot.hardware=beryllium