x86/vtx: Improvements to ept= command line handling

x86/vtx: Improvements to ept= command line handling

Switch parse_ept_param() to use the parse_boolean() infrastructure for more
consistency with related command line parameters.  Rename opt_pml_enabled to
opt_ept_pml for consistency with opt_ept_ad, and switch it to being bool

Drop the leading comment for parse_ept_param().  It is stale, and just repeats
the command line documentation.

For the command line documentation, rewrite it largely from scratch, updating
to the latest metadata style.  Document A/D first, including a note about
AVR41, and modify PML to note its dependency on A/D.

No practical changes to behaviour.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>