codec2: switch perferred linear allocator type by pool mask

The preferred linear buffer allocator could be switched between Gralloc BLOB
and ION by runtime property "debug.stagefright.c2-poolmask". ION should be
chosen as fallback allocator type if the pool mask property doesn't enable
the bit of Gralloc BLOB.

Bug: 143180475
Test: make libcodec2_vndk
Test: make libsfplugin_ccodec
Change-Id: I56fcca7f03660bca63a4974aa0f78a6d2a40e585