mtd: document ABI

We're missing a lot of important documentation in include/mtd/mtd-abi.h:

* add a simple description of each ioctl (feel free to expand!)
* give full explanations of recently added and modified operations
* explain the usage of "RAW" that appear in different modes and types of
  operations
* fix some comment style along the way

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index c2047b8..37d0827 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -79,7 +79,7 @@
  * @ooblen:	number of oob bytes to write/read
  * @oobretlen:	number of oob bytes written/read
  * @ooboffs:	offset of oob data in the oob area (only relevant when
- *		mode = MTD_OPS_PLACE_OOB)
+ *		mode = MTD_OPS_PLACE_OOB or MTD_OPS_RAW)
  * @datbuf:	data buffer - if NULL only oob data are read/written
  * @oobbuf:	oob data buffer
  *