fourcc: add ARGB for 32-bits RGBA with X11/BD components order
scale: add support for ARGB
yuvp: add conversion to ARGB
swscale: add ARGB conversions
avcodec: add ARGB mapping

Also remove bogus RGBA masks. Masks are only used for RGB formats - the
VLC chromas without implicitly fixed masks.
Xwd: fix 32-bits RGB chroma
XCB/screen: fix 32-bits screen capture format
XCB/x11: fix rendering to 32-bits surface
XCB/XVideo: fix 32-bits RGB support
vout: fix intermediate chroma when converting from YUVP then scaling
vout: allow ARGB for SPU