s4-common: set the bootloader msg offset

HTC offsets the bootloader message to 0x800 (2048) in /misc. This
prevents overwriting other stored variables in misc, such as the most
recently installed stock OS version.

Change-Id: I8499c9a3786820d105cc79968f010e16466124b3

BoardConfigCommon.mk

@@ -73,6 +73,7 @@ BOARD_RECOVERY_SWIPE := true
 TARGET_RECOVERY_PIXEL_FORMAT := RGBX_8888
 TARGET_RECOVERY_LCD_BACKLIGHT_PATH := \"/sys/class/leds/lcd-backlight/brightness\"
 BOARD_CUSTOM_RECOVERY_KEYMAPPING := ../../device/htc/s4-common/recovery/source/recovery_keys.c
+BOARD_RECOVERY_BLDRMSG_OFFSET := 2048
 
 # Charge mode
 BOARD_CHARGING_MODE_BOOTING_LPM := /sys/htc_lpm/lpm_mode