recovery: Allow custom bootloader msg offset in block misc

Squash of changes
  * Allow custom bootloader msg offset in block misc
    Change-Id: I6f3de1c2e3745c5535c3b95399abb8b2e2d01446

  * recovery: Move bldrmsg offset symbols to bootloader_message.cpp
    Change-Id: I2b902bcce7f5ca13472e0ac30ac01b4991294dbe

Adapted for Android.bp version of libbootloader_message

Change-Id: I5768660569d56b0d7c358f562e79483fd5f6db53

bootloader_message/Android.bp

@@ -26,4 +26,12 @@ cc_library_static {
         "libfs_mgr",
     ],
     export_include_dirs: ["include"],
+
+    product_variables: {
+        lineage: {
+            bootloader_message_offset : {
+                cflags: ["-DBOARD_RECOVERY_BLDRMSG_OFFSET=%d"],
+            },
+        },
+    },
 }

bootloader_message/bootloader_message.cpp

@@ -29,6 +29,16 @@
 #include <android-base/unique_fd.h>
 #include <fs_mgr.h>
 
+// Spaces used by misc partition are as below:
+// 0   - 2K     For bootloader_message
+// 2K  - 16K    Used by Vendor's bootloader (the 2K - 4K range may be optionally used
+//              as bootloader_message_ab struct)
+// 16K - 64K    Used by uncrypt and recovery to store wipe_package for A/B devices
+// Note that these offsets are admitted by bootloader,recovery and uncrypt, so they
+// are not configurable without changing all of them.
+static const size_t BOOTLOADER_MESSAGE_OFFSET_IN_MISC = BOARD_RECOVERY_BLDRMSG_OFFSET;
+static const size_t WIPE_PACKAGE_OFFSET_IN_MISC = 16 * 1024 + BOOTLOADER_MESSAGE_OFFSET_IN_MISC;
+
 static std::string get_misc_blk_device(std::string* err) {
   std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
                                                              fs_mgr_free_fstab);

bootloader_message/include/bootloader_message/bootloader_message.h

@@ -21,16 +21,6 @@
 #include <stddef.h>
 #include <stdint.h>
 
-// Spaces used by misc partition are as below:
-// 0   - 2K     For bootloader_message
-// 2K  - 16K    Used by Vendor's bootloader (the 2K - 4K range may be optionally used
-//              as bootloader_message_ab struct)
-// 16K - 64K    Used by uncrypt and recovery to store wipe_package for A/B devices
-// Note that these offsets are admitted by bootloader,recovery and uncrypt, so they
-// are not configurable without changing all of them.
-static const size_t BOOTLOADER_MESSAGE_OFFSET_IN_MISC = 0;
-static const size_t WIPE_PACKAGE_OFFSET_IN_MISC = 16 * 1024;
-
 /* Bootloader Message (2-KiB)
  *
  * This structure describes the content of a block in flash