contrib: dav1d: update to 1.4.2
Changes for 1.4.2 'Road Runner':
1.4.2 is a small release of dav1d, improving notably ARM, AVX-512 and PowerPC
- AVX2 optimizations for 8-tap and new variants for 6-tap
- AVX-512 optimizations for 8-tap and new variants for 6-tap
- Improve entropy decoding on ARM64
- New ARM64 optimizations for convolutions based on DotProd extension
- New ARM64 optimizations for convolutions based on i8mm extension
- New ARM64 optimizations for subpel and prep filters for i8mm