x86/vvmx: fix I/O and MSR bitmaps mapping

x86/vvmx: fix I/O and MSR bitmaps mapping

Currently Xen tries to map bitmaps during emulation of vmptrld and
vmwrite. This is wrong: a guest can store arbitrary values in those
fields.

Make bitmaps mapping happen only during a nested vmentry and only if
the appropriate execution controls are turned on by L1 hypervisor.

For performance reasons, Xen maps bitmaps only:

    1. During the first nested vmentry
    2. After L1 has changed an appropriate vmcs field
    3. After nvmx_purge_vvmcs() was previously called

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>