Add  MISC_MEMTAG_MODE_MEMTAG_OFF.

This can be used as a killswitch to disable MTE from userspace.

Change-Id: I28ab4357c9ac3e088776f92a0e1f7d390b4b0bdc
diff --git a/bootloader_message/include/bootloader_message/bootloader_message.h b/bootloader_message/include/bootloader_message/bootloader_message.h
index d58158d..8fba101 100644
--- a/bootloader_message/include/bootloader_message/bootloader_message.h
+++ b/bootloader_message/include/bootloader_message/bootloader_message.h
@@ -109,6 +109,7 @@
 #define MISC_MEMTAG_MODE_MEMTAG_ONCE 0x2
 #define MISC_MEMTAG_MODE_MEMTAG_KERNEL 0x4
 #define MISC_MEMTAG_MODE_MEMTAG_KERNEL_ONCE 0x8
+#define MISC_MEMTAG_MODE_MEMTAG_OFF 0x10
 
 #if (__STDC_VERSION__ >= 201112L) || defined(__cplusplus)
 static_assert(sizeof(struct misc_virtual_ab_message) == 64,