KVM: MMU: Modify kvm_shadow_walk.entry to accept u64 addr

KVM: MMU: Modify kvm_shadow_walk.entry to accept u64 addr

EPT is 4 level by default in 32pae(48 bits), but the addr parameter
of kvm_shadow_walk->entry() only accept unsigned long as virtual
address, which is 32bit in 32pae. This result in SHADOW_PT_INDEX()
overflow when try to fetch level 4 index.

Fix it by extend kvm_shadow_walk->entry() to accept 64bit addr in
parameter.

Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>