Add a comment and while there, fix trailing whitespace.
- Output a summary of optional VT-x features in dmesg similar to CPU
  features.  If bootverbose is enabled, a detailed list is provided;
  otherwise, a single-line summary is displayed.
- Add read-only sysctls for optional VT-x capabilities used by bhyve
  under a new hw.vmm.vmx.cap node. Move a few exiting sysctls that
  indicate the presence of optional capabilities under this node.

CR:		https://phabric.freebsd.org/D498
Reviewed by:	grehan, neel
MFC after:	1 week