x86/x86-64 MMU PAE fixes

x86/x86-64 MMU PAE fixes

This patch fixes MMU emulation in PAE mode for > 4GB physical addresses:
- a20_mask should have the correct size to not clear the high part of
  the addresses.
- PHYS_ADDR_MASK should not clear the high part of the addresses.
- pdpe, pde and pte could be located anywhere in memory on x86-64, but
  only in the first 4GB on x86, define their pointer to as target_ulong.
- pml4e_addr could be located anywhere in memory, define its pointer
  as uint64_t.
- paddr represents a physical address and thus should be of type
  target_phys_addr_t.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4239 c046a42c-6fe2-441c-8c8c-71466251a162