Documentation/vm: include kdocs from highmem*.h into highmem.rst

kernel-docs that are in include/linux/highmem.h and in
include/linux/highmem-internal.h should be included in highmem.rst.

Use kdocs directives to include the above-mentioned comments into
highmem.rst.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Fabio M. De Francesco <[email protected]>
Acked-by: Mike Rapoport <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Suggested-by: Ira Weiny <[email protected]>
Reviewed-by: Sebastian Andrzej Siewior <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Peter Collingbourne <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: xp4ns3

Documentation/vm/highmem.rst

@@ -145,3 +145,10 @@ The general recommendation is that you don't use more than 8GiB on a 32-bit
 machine - although more might work for you and your workload, you're pretty
 much on your own - don't expect kernel developers to really care much if things
 come apart.
+
+
+Functions
+=========
+
+.. kernel-doc:: include/linux/highmem.h
+.. kernel-doc:: include/linux/highmem-internal.h