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.
dsputil: Remove disabled avg_no_rnd_qpel leftovers
dsputil.h: Clean up comments
dsputil.h: K&R formatting cosmetics
dsputil: K&R formatting cosmetics
dsputil: Merge variable declarations and initializations
dsputil: cosmetics: Lose camelCase on ff_cropTbl and ff_squareTbl names

Also switch from "tbl" to "tab" name suffixes.
rnd_avg.h: K&R formatting cosmetics
dsputil_template: K&R formatting cosmetics
dsputilenc_mmx: Merge two assignment blocks with identical conditions