Documentation: x86: convert x86_64/machinecheck to reST

This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/x86/x86_64/index.rst

@@ -13,3 +13,4 @@ x86_64 Support
    5level-paging
    fake-numa-for-cpusets
    cpu-hotplug-spec
+   machinecheck

Documentation/x86/x86_64/machinecheck.rst

@@ -1,5 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
 
-Configurable sysfs parameters for the x86-64 machine check code.
+===============================================================
+Configurable sysfs parameters for the x86-64 machine check code
+===============================================================
 
 Machine checks report internal hardware error conditions detected
 by the CPU. Uncorrected errors typically cause a machine check
@@ -16,14 +19,13 @@ log then mcelog should run to collect and decode machine check entries
 from /dev/mcelog. Normally mcelog should be run regularly from a cronjob.
 
 Each CPU has a directory in /sys/devices/system/machinecheck/machinecheckN
-(N = CPU number)
+(N = CPU number).
 
 The directory contains some configurable entries:
 
-Entries:
-
 bankNctl
-(N bank number)
+	(N bank number)
+
 	64bit Hex bitmask enabling/disabling specific subevents for bank N
 	When a bit in the bitmask is zero then the respective
 	subevent will not be reported.