doc: blk-ioprio: Bring the doc in line with the implementation

Our system administrator have noted that the names 'rt-to-be' and
'all-to-idle' in the I/O priority policies table appeared without
explanations, leading to confusion. Let's bring these names in line
with the naming in the 'attribute' section.

Additionally,
1. Correct the interface name to 'io.prio.class'.
2. Add a table entry of 'promote-to-rt' for consistency.
3. Fix a typo of 'priority'.

Suggested-by: Yingfu Zhou <yingfu.zhou@shopee.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231012024228.2161283-1-yizhou.tang@shopee.com

Author: Tang Yizhou

Documentation/admin-guide/cgroup-v2.rst

@@ -2023,7 +2023,7 @@ IO Priority
 ~~~~~~~~~~~
 
 A single attribute controls the behavior of the I/O priority cgroup policy,
-namely the blkio.prio.class attribute. The following values are accepted for
+namely the io.prio.class attribute. The following values are accepted for
 that attribute:
 
   no-change
@@ -2052,9 +2052,11 @@ The following numerical values are associated with the I/O priority policies:
 +----------------+---+
 | no-change      | 0 |
 +----------------+---+
-| rt-to-be       | 2 |
+| promote-to-rt  | 1 |
 +----------------+---+
-| all-to-idle    | 3 |
+| restrict-to-be | 2 |
++----------------+---+
+| idle           | 3 |
 +----------------+---+
 
 The numerical value that corresponds to each I/O priority class is as follows:
@@ -2074,7 +2076,7 @@ The algorithm to set the I/O priority class for a request is as follows:
 - If I/O priority class policy is promote-to-rt, change the request I/O
   priority class to IOPRIO_CLASS_RT and change the request I/O priority
   level to 4.
-- If I/O priorityt class is not promote-to-rt, translate the I/O priority
+- If I/O priority class policy is not promote-to-rt, translate the I/O priority
   class policy into a number, then change the request I/O priority class
   into the maximum of the I/O priority class policy number and the numerical
   I/O priority class.