build: Drop stray mpc8 decoder dependency on dsputil
build: Drop stray PNG decoder dependency on dsputil
build: Drop stray MLP decoder dependency on dsputil
build: Drop stray MJPEG encoder dependency on dsputil
build: Drop stray LPC dependency on dsputil
ffv1: Drop bogus dependency on dsputil

ffv1 does not use any part of the dsputil framework.
configure: Add explicit dsputil dependency to mpegvideoenc

Previously, it was an implicit dependency through mpegvideo. Change
this, as implicit dependencies can cause all sorts of trouble.
build: Record dependency of eatqi decoder on dsputil
Remove all SH4 architecture optimizations

SH4 has been end-of-lifed and no more test machines are available.
Remove all SPARC architecture optimizations

SPARC is no longer being used in any multimedia-related fields and the
VIS optimizations only represent a maintenance burden.
x86: mpegvideoenc: Remove some remnants of the long-gone libmpeg2 IDCT
dsputil: Remove prototypes for nonexisting optimization functions
dsputil: Drop ff_check_alignment() function

The function is supposed to confirm that the compiler provided enough
alignment, but in practice it is only run in certain code paths and
insufficient alignment problems are restricted to legacy compilers.
dsputil: Move intreadwrite.h #include from header file to .c files
ppc: Add some missing headers
x86: Add some more missing headers
arm: dsputil: Add a bunch of missing #includes
Update dsputil- and SIMD-related comments to match reality more closely
x86: h264_idct_10_bit: Use proper type in function prototype comments
x86: Make function prototype comments in assembly code consistent

This helps grepping for functions, among other things.