multirom: trampoline: Support creating a bootdevice symlink

 * Use the MR_DEVICE_BOOTDEVICE := /dev/block/platform...
    configuration to create a symlink with /dev/block/bootdevice

Change-Id: I3e4c6c8e1f9e9861d2f87b689d9633f891f35a6f

Author: AdrianDC

trampoline/Android.mk

@@ -37,6 +37,9 @@ endif
 ifeq ($(MR_DEV_BLOCK_BOOTDEVICE),true)
     LOCAL_CFLAGS += -DMR_DEV_BLOCK_BOOTDEVICE
 endif
+ifneq ($(MR_DEVICE_BOOTDEVICE),)
+    LOCAL_CFLAGS += -DMR_DEVICE_BOOTDEVICE="\"$(MR_DEVICE_BOOTDEVICE)\""
+endif
 
 ifneq ($(MR_DEVICE_HOOKS),)
 ifeq ($(MR_DEVICE_HOOKS_VER),)

trampoline/devices.c

@@ -660,6 +660,9 @@ static char **parse_platform_block_device(struct uevent *uevent)
         links[link_num] = NULL;
 #endif
 
+#ifdef MR_DEVICE_BOOTDEVICE
+    symlink(MR_DEVICE_BOOTDEVICE, "/dev/block/bootdevice");
+#endif
     return links;
 }