package/mplayer: add x86-specific configure options

The mplayer configure script tries to detect the capabilities of the CPU
used by probing the host CPU. This leads to compilation failures if the
target CPU has lesser features, like missing mmx support for
BR2_x86_i686=y:

Checking for CPU vendor ... GenuineIntel (6:58:9)
Checking for CPU type ...  Intel(R) Core(TM) i7-3770S CPU @ 3.10GHz
Checking for kernel support of sse ... yes
Checking for kernel support of sse2 ... yes
Checking for kernel support of sse3 ... yes
Checking for kernel support of ssse3 ... yes
Checking for kernel support of sse4_1 ... yes
Checking for kernel support of sse4_2 ... yes
Checking for kernel support of avx ... yes

For this patch I copied most of ffmpeg configure options for x86 CPUs
because mplayer contains its own copy of ffmpeg.

Fixes
http://autobuild.buildroot.net/results/c5a/c5a722607ec9797c317b63b0fd3235608a340c98/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>