host msc: call read_capacity as part of enumeration

- add tuh_msc_get_block_count(), tuh_msc_get_block_size()
- rename tuh_msc_mounted_cb/tuh_msc_unmounted_cb to
tuh_msc_mount_cb/tuh_msc_unmount_cb to match device stack naming
- change tuh_msc_is_busy() to tuh_msc_ready()
- add CFG_TUH_MSC_MAXLUN (default to 4) to hold lun capacities
- add host msc configured to for state check.

lib/fatfs/diskio.c

@@ -48,7 +48,7 @@ static DSTATUS disk_state[CFG_TUSB_HOST_DEVICE_MAX];
 static DRESULT wait_for_io_complete(uint8_t usb_addr)
 {
   // TODO with RTOS, this should use semaphore instead of blocking
-  while ( tuh_msc_is_busy(usb_addr) )
+  while ( !tuh_msc_ready(usb_addr) )
   {
     // TODO should have timeout here
     #if CFG_TUSB_OS != OPT_OS_NONE