When the code for detecting the number of CPUs present was moved
the headers necessary to compile the AltiVec detection code on
OpenBSD/powerpc was mistakenly removed so this puts the headers
back as appropriate.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

It seems to also be used for chroma upsampling.
It fixes #5751.

There are no reasons to only apply them to the first one. Certainly
some options might only make sense with a single item. But then it
really boils down to having only one item. Some options *do* make
sense for all (>1) items.

i_prog takes its value from i_num_pmt which can't be negative, nor > 64

cosmetics, reindent

ref: rfc 3555

Note that MUX_MIME_TYPE is currently never used

simplify CSA setup

it's in libdvbpsi since 2004