refine deblocking filter
remove getNumPartInCU() and replace it with macro
asm: avx2 assembly code for idct8x8
analysis: hoist local function into anonymous namespace (file local)
analysis: remove unused LAMBDA_PARTITION_SELECT
analysis: coding style and comment nits
analysis: remove #define conditionals for control flow

The non-default paths are not being tested (or even compiled) and are thus
assumed broken. The defines simply make the code harder to read.
analysis: more style nits, code simplifications. no behavior change
Removed unnecessary call to loadCTUData
asm: avx2 assembly code for idct32x32