multimedia/libx264: Move libx264 stdin.h patch to x264 port

Move the libx264 patch for stdint.h handling on FreeBSD to the multimedia/x264
port, as FILESDIR is inherited from there, thus causing the patch not to be
applied.

Reported by: kwm
Reviewed by: kwm
Tested by: kwm
Differential Revision: https://reviews.freebsd.org/D3168