The EPT present/writable bits use the same position as normal
pagetable bits.

Since direct_map passes ACC_ALL to mmu_set_spte, thus always setting
the writable bit on sptes, use the generic PT_PRESENT shadow_base_pte.

Also pass present/writable error code information from EPT violation
to generic pagefault handler.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>