h261: Move ff_h261_rl_table_store declaration to header file
h261: Remove H.261 loop filter from dsputil

There is no arch-optimized version of the H.261 loop filter and there
likely will never be, so the dsputil overhead does not give any benefit.
h261: Move function declarations to h261.h
h261: K&R formatting and prettyprinting cosmetics
h261: cosmetics: Move functions to avoid forward declarations
h261: Move mvmap table to the only place it is used