meram.conf: remove the description of reserving MERAM memory blocks

The description 'reserved 0 639' in meram.conf must be inappropriate
as the default configuration since amount of MERAM memory may be
different depending on each SoC implementation.
suppress a compiler warning on implicit type casting

The 'unsigned long' type could be different from 'unsigned int'.
fix a careless memory leak in parse_config_file()

Free the 'fields' arrays when they are no longer needed
fix an implicit memory leak in parse_config_file()

The strdup() call involves memory allocation internally and
the caller must release the allocated memory block responsibly.
clear 'static' pointer value whenever the pointer is freed

This is necessary if the library is to be openeded multiple times.