docs: Fix HVM user documentation

docs: Fix HVM user documentation

Summary of changes:

- replaced VMX with HVM
- added AMD as a vendor of HVM capable processors
- removed LibVNCServer as a requirement for HVM builds
- fixed name of HVM example file
- changed default value of acpi, apic and pae options
- added hap option
- removed reference to cdrom option and integrated it into "disk"
- improved examples for disk option
- replaced vncviewer option with vncconsole
- removed obsolete ne2000 option
- replaced enable-audio with soundhw
- fixed dd usage for creating sparse files (count=0)
- remove acpi=0 hint for Windows guests
- removed reference to (obsolete?) -f option for xm create
- made shutdown advice less Linux centric
- removed comment about save/restore and migration not yet ready

Signed-off-by: Andre Przywara <andre.przywara@amd.com>