fs_mgr: Allow overriding the super partition name via the kernel commandline.

For retrofit devices where the super partition is not called "super",
this allows the correct partition to be passed via the kernel
command-line, i.e.:

  androidboot.super_partition=system

Since retrofitting is only supported for A/B devices, we assume that
a partition named this way must be slot-suffixed.

Bug: 116802789
Test: manual test
Change-Id: I930dbbd397d5552e9ded89baa5a7bb0e63c67426
diff --git a/fs_mgr/fs_mgr_priv.h b/fs_mgr/fs_mgr_priv.h
index 5e83cfb..23a92d3 100644
--- a/fs_mgr/fs_mgr_priv.h
+++ b/fs_mgr/fs_mgr_priv.h
@@ -39,11 +39,13 @@
 #define LINFO    LOG(INFO) << FS_MGR_TAG
 #define LWARNING LOG(WARNING) << FS_MGR_TAG
 #define LERROR   LOG(ERROR) << FS_MGR_TAG
+#define LFATAL LOG(FATAL) << FS_MGR_TAG
 
 // Logs a message with strerror(errno) at the end
 #define PINFO    PLOG(INFO) << FS_MGR_TAG
 #define PWARNING PLOG(WARNING) << FS_MGR_TAG
 #define PERROR   PLOG(ERROR) << FS_MGR_TAG
+#define PFATAL PLOG(FATAL) << FS_MGR_TAG
 
 #define CRYPTO_TMPFS_OPTIONS "size=512m,mode=0771,uid=1000,gid=1000"