docs: add some new files to their respective index.rst files

There were some new file additions for Kernel 5.7 and 5.8
that weren't added at the corresponding index file.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9fd4d04f0d122ff38b5342a0098d99cc2f546652.1599660067.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/nvdimm/index.rst

@@ -10,3 +10,4 @@ Non-Volatile Memory Device (NVDIMM)
    nvdimm
    btt
    security
+   firmware-activate

Documentation/firmware-guide/acpi/index.rst

@@ -26,3 +26,4 @@ ACPI Support
    lpit
    video_extension
    extcon-intel-int3496
+   intel-pmc-mux

Documentation/hwmon/index.rst

@@ -158,6 +158,7 @@ Hardware Monitoring Kernel Drivers
    smsc47b397
    smsc47m192
    smsc47m1
+   sparx5-temp
    tc654
    tc74
    thmc50

Documentation/vm/index.rst

@@ -29,6 +29,7 @@ descriptions of data structures and algorithms.
    :maxdepth: 1
 
    active_mm
+   arch_pgtable_helpers
    balance
    cleancache
    free_page_reporting