Combining integer and fractional parts of mvs for entropy coding.

Combining encode_nmv_component with encode_nmv_component_fp
and read_nmv_component with read_nmv_component_fp. Bitstream is slightly
changed (only the order of bits), here are the results on test sets:
stdhd: +0.047, yt: -0.038, derf: +0.001, hd: -0.011.

Change-Id: I1be312e976796df78ca63368702d0ee19f2b8c50