Add scempegbase stuff

Find in homebrew game
I guest parameter of sceMpegbase_BEA18F91  by JPCSPTrace log
Seem sceMpegbase_BEA18F91 make mpeg buffer  for sceMpegAvcDecode

JPCSPTrace log:
https://gist.github.com/sum2012/1bedb4380065919edb03
PPSSPP Modify log:
https://gist.github.com/sum2012/5047fc1f37da391c72e2