Miscelleneous changes in detokenize for speed

Changes to reduce branching in detokenization  in order
to improve decode speed.

Change-Id: I23a74d072cc14d99f6fc054c1e6a72021e777903
Add back vp9_short_idct32x32_1_add_neon which is deleted in
cleanup I63df79a13cf62aa2c9360a7a26933c100f9ebda3.

Change-Id: I034848cf05031618818f7df2e7f9c35102686948
disable avx/avx2 for old versions of MSVC

Change-Id: Ifb40757c9c6b353482cfeef929af282ee0136c6c
Fix the variable naming in encode_block

The term x represents macroblock pointer across encode_block. Change
the two local variable names to avoid confusion.

Change-Id: Ic732e73023525d673c0a678ed2708ac1edf5a3f9
Merge "disable avx/avx2 for old versions of MSVC"
Merge "Miscelleneous changes in detokenize for speed"
Merge "Fix the variable naming in encode_block"
Merge "Add back vp9_short_idct32x32_1_add_neon which is deleted in cleanup I63df79a13cf62aa2c9360a7a26933c100f9ebda3."