[SPARK-3739] [SQL] Update the split num base on block size for table scanning

Source file input split is probably better based on block size of HDFS, or the setting of 'mapred.map.tasks' while scanning Hive table, rather than 'defaultMinPartitions'. 
Checkout http://grepcode.com/file/repository.cloudera.com/content/repositories/releases/org.apache.hadoop/hadoop-core/2.3.0-mr1-cdh5.1.0/org/apache/hadoop/mapred/FileInputFormat.java#203 for how handles the input splits by default.

Currently, there will be 2 splits for small table file in scanning, which probably causes performance issue  or different result with Hive in query.