mempool: add the minimum size configuration of mempool

The minimum size of mempool can be configured through CONFIG_MM_MPOOL_MINISIZE

Signed-off-by: liwenxiang1 <liwenxiang1@xiaomi.com>

mm/tlsf/mm_tlsf.c

@@ -1021,7 +1021,11 @@ mm_initialize_pool(FAR const char *name,
 
       for (i = 0; i < MEMPOOL_NPOOLS; i++)
         {
+#  if CONFIG_MM_MIN_BLKSIZE != 0
+          poolsize[i] = (i + 1) * CONFIG_MM_MIN_BLKSIZE;
+#  else
           poolsize[i] = (i + 1) * tlsf_align_size();
+#  endif
         }
 
       def.poolsize        = poolsize;