sad_test: fix vp8-only build

ROUND_POWER_OF_TWO() is defined in vp9 headers currently, avoid it in
non-high-bitdepth code

Change-Id: Ic28b8f95ef7964800475ee8b35be5f9cea9afab6
vp9_ethread: move max/min partition size to mb struct

The max_partition_size and max_partition_size are set at the
beginning while setting speed features, and then adjusted at
SB level. Moving them to mb struct ensures there is a local
copy for each thread.

Change-Id: I7dd08dc918d9f772fcd718bbd6533e0787720ad4
Merge "vp9_ethread: move max/min partition size to mb struct"
Merge "sad_test: fix vp8-only build"