drm/i915/gvt: Drop final dependencies on KVM internal details

Open code gpa_to_gfn() in kvmgt_page_track_write() and drop KVMGT's
dependency on kvm_host.h, i.e. include only kvm_page_track.h.  KVMGT
assumes "gfn == gpa >> PAGE_SHIFT" all over the place, including a few
lines below in the same function with the same gpa, i.e. there's no
reason to use KVM's helper for this one case.

No functional change intended.

Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Link: https://lore.kernel.org/r/20230729013535.1070024-30-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>