docs: hwmon: vexpress: convert to ReST format

Convert vexpress to ReST format, in order to allow it to
be parsed by Sphinx.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>