[BugFix] Multiboot Database duplicate files

When the sd card is mounted into the root namespace the database
picks up files through both paths

previously we hid the mounted drive but this causes issues with users
databases when the drive letter changes

Adds a way to keep track of volumes mounted in the root namespace

Hides the enumerated volume in root

Database:
we can just parse the root directory ('/') and get to any mounted
volume but we can also enumerate a volume in the root directory
when this occurs it leads to multiple entries since the files can
be reached through multiple paths ex, /Foo could also be /SD1/Foo
Instead we will attempt to rewrite the root with any non-hidden volumes
failing that just leave the paths alone

Change-Id: I7bdba8cfaf63902d2a3852d28484bcf8ca317ebd

uisimulator/common/filesystem-sim.c

@@ -843,3 +843,8 @@ int os_volume_path(IF_MV(int volume, ) char *buffer, size_t bufsize)
 
     return sim_get_os_path(buffer, tmpbuf, bufsize);
 }
+
+const char* sim_root_realpath(void)
+{
+    return PATH_ROOTSTR;
+}