Fix building with PCH disabled.
Merge pull request #1649 from rohit-n/build-pch

Fix building with PCH disabled.
VideoCommon: fix include order
Think of this as rough draft. Taking suggestions to make it robust, error free, and prettier!

For more information:
https://docs.google.com/document/d/1tBEgsJh7QiwNwepXI0eobfK3U8LkJButSyeuFt1degM/edit?usp=sharing

removed: SSE includes

added: 16bit -> float -> 16bit functions
added: linear interpolator and high-quality interpolator functions (including Resampler class)
added: dithering

changed: renamed variables and reformatted a few things to fit with style guide
changed: use s16, u16, s32, u32 etc
changed: store samples and do all computations as floats
changed: volume from 0 - 255
Fixed some styling stuff (whitespace and brackets)

Moved #defines to static const (did I do it right?)
Moved inline fx's to header file
changed math.h to cmath
It seems that all of the other Dolphin-emu files that uses M_PI define it like this. (MatrixMath.h, DPL2Decode.cpp).
Moved stuff around to consolidate.