1. Do not do map when MppBuffer alloc or import. Only map when user requires a
user pointer. This will save a lot of vma resource especially when buffer is
very large.
2. Fix error in mpp_dec thread which use info.ptr directly.
3. Use external fd on import (have risk of external user close fd on hw work)
Change-Id: I28225f6ba28afa3e9475e605bf971348dcef185a
Signed-off-by: Herman Chen <herman.chen@rock-chips.com>