Move firstpass motion map to stats packet

The first implementation of the firstpass motion map for motion
compensated temporal filtering created a file, fpmotionmap.stt,
in the current working directory. This was not safe for multiple
encoder instances. This patch merges this data into the first pass
stats packet interface, so that it is handled like the other
(numerical) firstpass stats.

The new stats packet is defined as follows:
    Numerical Stats (16 doubles) -- 128 bytes
    Motion Map                   -- 1 byte / Macroblock
    Padding                      -- to align packet to 8 bytes

The fpmotionmap.stt file can still be generated for debugging
purposes in the same way that the textual version of the stats
are available (defining OUTPUT_FPF in firstpass.c)

Change-Id: I083ffbfd95e7d6a42bb4039ba0e81f678c8183ca