Update pmm.c, pmap.c; Added asm functions; Renamed mm_types.h to mm.h

Implemented pmm_reserve function in pmm.c to mark pages used by the
kernel
Added _libasm.s which implements some basic functions only available via
ARM assembly
Renamed mm_types.h to mm.h
Partially implemented pmap_steal_memory
Update bithacks.c

bit_find_contiguous_zeros now searches the bitmap starting from bit 0 by
using rbit in conjunction with clz