block: change config option name for cmdline partition parsing

Recently commit bab55417b10c ("block: support embedded device command
line partition") introduced CONFIG_CMDLINE_PARSER.  However, that name
is too generic and sounds like it enables/disables generic kernel boot
arg processing, when it really is block specific.

Before this option becomes a part of a full/final release, add the BLK_
prefix to it so that it is clear in absence of any other context that it
is block specific.

In addition, fix up the following less critical items:
 - help text was not really at all helpful.
 - index file for Documentation was not updated
 - add the new arg to Documentation/kernel-parameters.txt
 - clarify wording in source comments

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Cai Zhiyong <caizhiyong@huawei.com>
Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/block/cmdline-partition.txt b/Documentation/block/cmdline-partition.txt
index 2bbf4cc..525b9f6 100644
--- a/Documentation/block/cmdline-partition.txt
+++ b/Documentation/block/cmdline-partition.txt
@@ -1,9 +1,9 @@
-Embedded device command line partition
+Embedded device command line partition parsing
 =====================================================================
 
-Read block device partition table from command line.
-The partition used for fixed block device (eMMC) embedded device.
-It is no MBR, save storage space. Bootloader can be easily accessed
+Support for reading the block device partition table from the command line.
+It is typically used for fixed block (eMMC) embedded devices.
+It has no MBR, so saves storage space. Bootloader can be easily accessed
 by absolute address of data on the block device.
 Users can easily change the partition.