Add 3 functions to utils_memory for getting some usage info of hugepages.

get_num_anon_huge_pages(pid) : get the anonhugepages' usage amount of a progress
get_num_huge_pages_free() : get the number of free hugepages
get_num_huge_pages_rsvd() : get the number of rsvd hugepages
Oh I don't mean these two function is related. Just mean that both this function and get_num_huge_pages_rsvd() can call read_from_meminfo() directly.