doc-rst: fe_property_parameters: improve descriptions

doc-rst: fe_property_parameters: improve descriptions

The asterisks cause parsing warnings with Sphinx:
	Documentation/linux_tv/media/dvb/fe_property_parameters:954: WARNING: Inline substitution_reference start-string without end-string.
	/devel/v4l/patchwork/Documentation/linux_tv/media/dvb/fe_property_parameters:993: WARNING: Inline emphasis start-string without end-string.

On the first warning, the ISDB-T layer enabled description is a
kind of ackward. Improve it.

For the second one, IMHO, it is clearer to use [A-C], as it
shows what are the real possibilities, than using asterisk.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>