Fix L2 PTE access permissions management.

Keep following access permissions:

APX     AP     Kernel     User
 1      01       R         N
 1      10       R         R
 0      01      R/W        N
 0      11      R/W       R/W

Avoid using reserved in ARMv6 APX|AP settings:
- In case of unprivileged (user) access without permission to write,
  the access permission bits were being set to reserved for ARMv6
  (but valid for ARMv7) value of APX|AP = 111.

Fix-up faulting userland accesses properly:
- Wrong condition statement in pmap_fault_fixup() caused that
  any genuine, unprivileged access was being fixed-up instead of
  just skip doing anything and return. Staring from now we ensure
  proper reaction for illicit user accesses.

L2_S_PROT_R and L2_S_PROT_U names might be misleading as they do not
reflect real permission levels. It will be clarified in following
patches (switch to AP[2:1] permissions model).

Obtained from: Semihalf
Fix byte order of ATA WWN when converting it to SCSI LUN ID.
Fix page reference emulation on ARMv6 and v7

Submitted by: Zbigniew Bodek
Obtained from: Semihalf