arm: fix compilation for HIGH_BIT_DEPTH

Caused by conflicting prototypes for neon predict functions added in
babcab to arm/predict.h.

Remove the duplicate prototypes from arm/predict-c.c and change the type
from pixel to uint8_t since there are no plans for high bit depth arm
neon optimizations.
aarch64: require PIC in shared mode
arm: move all .macro/.endm to column 0
arm: do not export every asm function

Based on Libav's libavutil/arm/asm.S. Also prevents having the same
label twice for every function on systems not defining EXTERN_ASM.
Clang's integrated assembler does not like it.
arm: correct x264_mc_chroma_neon function declaration
arm: use the weight_fn_t typedef for mc weight function arrays
x86: add missing initializations for high bit-depth variance
x86: add missing initialization for high bit-depth sa8d_satd
x86util: XOP optimized HADDD
x86: XOP pixel_ssd_nv12_core
x86: XOP pixel_sad_{x3, x4} high bit-depth
Improve 2-pass VBV

Should now apply VBV underflow logic to B-frames too, which may fix some
instances of VBV misprediction.