mmc: queue: append partition subname to queue thread name

For example, an eMMC with 2 boot partitions will have 3 threads.
The names change from:

   40 ?        00:00:00 mmcqd/0
   41 ?        00:00:00 mmcqd/0
   42 ?        00:00:00 mmcqd/0

to:

   40 ?        00:00:00 mmcqd/0
   41 ?        00:00:00 mmcqd/0boot0
   42 ?        00:00:00 mmcqd/0boot1

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andrei Warkentin <andreiw@motorola.com>
Signed-off-by: Chris Ball <cjb@laptop.org>