Added comments and fixed something.

Added comments to source files.
 - lpae.h, lpae.c, mm.c, mm.h, smp.h, vmm.h and vmm.c.
Fixed TTBL level 1 mask bit.
 - In lpae.c file. TTBL_L2_OUTADDR_MASK
  - 0x000000FFEC000000ULL -> 0x000000FFC0000000ULL