KVM: VMX: Make CR0.WP a guest owned bit

Guests like grsecurity that make heavy use of CR0.WP to implement kernel
level W^X will suffer from the implied VMEXITs.

With EPT there is no need to intercept a guest change of CR0.WP, so
simply make it a guest owned bit if we can do so.

This implies that a read of a guest's CR0.WP bit might need a VMREAD.
However, the only potentially affected user seems to be kvm_init_mmu()
which is a heavy operation to begin with. But also most callers already
cache the full value of CR0 anyway, so no additional VMREAD is needed.
The only exception is nested_vmx_load_cr3().

This change is VMX-specific, as SVM has no such fine grained control
register intercept control.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230322013731.102955-7-minipli@grsecurity.net
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

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