vmw_balloon: support 64-bit memory limit

Currently, the balloon driver would fail to run if memory is greater
than 16TB of vRAM. Previous patches have already converted the balloon
target and size to 64-bit, so all that is left to do add is to avoid
asserting memory is smaller than 16TB if the hypervisor supports 64-bits
target.

The driver advertises a new capability VMW_BALLOON_64_BITS_TARGET.
Hypervisors that support 16TB of memory or more will report that this
capability is enabled.

Signed-off-by: Xavier Deguillard <xdeguillard@vmware.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>