KVM: nVMX: Do not inherit quadrant and invalid for the root shadow EPT

Explicitly zero out quadrant and invalid instead of inheriting them from
the root_mmu.  Functionally, this patch is a nop as we (should) never
set quadrant for a direct mapped (EPT) root_mmu and nested EPT is only
allowed if EPT is used for L1, and the root_mmu will never be invalid at
this point.

Explicitly setting flags sets the stage for repurposing the legacy
paging bits in role, e.g. nxe, cr0_wp, and sm{a,e}p_andnot_wp, at which
point 'smm' would be the only flag to be inherited from root_mmu.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>