x86/hvm: Drop restore boolean from hvm_cr4_guest_valid_bits()

x86/hvm: Drop restore boolean from hvm_cr4_guest_valid_bits()

Previously, migration was reordered so the CPUID data was available before
register state.  nestedhvm_enabled() has recently been made accurate for the
entire lifetime of the domain.

Therefore, we can drop the bodge in hvm_cr4_guest_valid_bits() which existed
previously to tolerate a guests' CR4 being set/restored before
HVM_PARAM_NESTEDHVM.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>