xpmem: porting xpmem v2.6.3

implement xpmem_make, xpmem_remove

kernel/include/syscall.h

@@ -392,6 +392,7 @@ extern struct tod_data_s tod_data;	/* residing in arch-dependent file */
 
 void reset_cputime();
 void set_cputime(int mode);
+int do_munmap(void *addr, size_t len);
 intptr_t do_mmap(intptr_t addr0, size_t len0, int prot, int flags, int fd,
 		off_t off0);
 void clear_host_pte(uintptr_t addr, size_t len);