KVM: x86/mmu: Always walk guest PTEs with WRITE access when unprotecting

KVM: x86/mmu: Always walk guest PTEs with WRITE access when unprotecting

When getting a gpa from a gva to unprotect the associated gfn when an
event is awating reinjection, walk the guest PTEs for WRITE as there's no
point in unprotecting the gfn if the guest is unable to write the page,
i.e. if write-protection can't trigger emulation.

Note, the entire flow should be guarded on the access being a write, and
even better should be conditioned on actually triggering a write-protect
fault.  This will be addressed in a future commit.

Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20240831001538.336683-14-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>