Added mount/unmount to FATFileSystem

Added virtual mount()/unmount() methods to FATFileSystem to allow users
to swap removable disks.

libraries/fs/fat/FATFileSystem.cpp

@@ -130,3 +130,15 @@ int FATFileSystem::mkdir(const char *name, mode_t mode) {
     FRESULT res = f_mkdir(name);
     return res == 0 ? 0 : -1;
 }
+
+int FATFileSystem::mount() {
+    FRESULT res = f_mount(_fsid, &_fs);
+    return res == 0 ? 0 : -1;
+}
+
+int FATFileSystem::unmount() {
+    if (disk_sync())
+        return -1;
+    FRESULT res = f_mount(_fsid, NULL);
+    return res == 0 ? 0 : -1;
+}

libraries/fs/fat/FATFileSystem.h

@@ -44,6 +44,8 @@ public:
     virtual int format();
     virtual DirHandle *opendir(const char *name);
     virtual int mkdir(const char *name, mode_t mode);
+    virtual int mount();
+    virtual int unmount();
 
     virtual int disk_initialize() { return 0; }
     virtual int disk_status() { return 0; }