Added comments and fixed address masking definition.

Added comments - lpae.h, lpae.c, smp.h, mm.h, mm.c, vmm.h and vmm.c.
Fixed address masking definition. - lpae.c
TTBL_L1_OUTADDR_MASK    0x000000FFEC000000ULL -> 0x000000FFC0000000ULL
Added MMU_ON and MMU_OFF definition.
Change function name. - vmm.c
void vmm_stage2_enable -> static void stage2_mmu_enable