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