x86/vvmx: Fix nested virt on VMCS-Shadow capable hardware

x86/vvmx: Fix nested virt on VMCS-Shadow capable hardware

c/s e9986b0dd "x86/vvmx: Simplify per-CPU memory allocations" had the wrong
indirection on its pointer check in nvmx_cpu_up_prepare(), causing the
VMCS-shadowing buffer never be allocated.  Fix it.

This in turn results in a massive quantity of logspam, as every virtual
vmentry/exit hits both gdprintk()s in the *_bulk() functions.

Switch these to using printk_once(), but still only in debug builds.  The size
of the buffer is chosen at compile time, so complaining about it repeatedly is
of no benefit.

Finally, drop the runtime NULL pointer checks.  It is not terribly appropriate
to be repeatedly checking infrastructure which is set up from start-of-day,
and in this case, actually hid the above bug.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>