docs/boot-time-mm: fix kernel-doc directive for including all but DOC:

There were several rounds of the patches that enabled "functions" directive
with no parameters in kerneldoc.py to allow including all the kernel-doc
comments except the DOC: sections.

Yet, the boot-time-mm.rst sneaked in with the older version of that
directive and was not updated. Update it now.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/boot-time-mm.rst

@@ -76,7 +76,7 @@ These interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n``
 
 .. kernel-doc:: include/linux/bootmem.h
 .. kernel-doc:: mm/bootmem.c
-   :nodocs:
+   :functions:
 
 Memblock specific API
 ---------------------
@@ -89,4 +89,4 @@ really happens under the hood.
 
 .. kernel-doc:: include/linux/memblock.h
 .. kernel-doc:: mm/memblock.c
-   :nodocs:
+   :functions: