Fix various minor issues

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
g2d: Blitter was clearing with the wrong color

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
g2d: Change format details to use bits per pixel instead of bytes per pixel

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Move kernel header path checks into main wscript

PxP code will also require the paths

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
pxp: add PxP-based blitter video sink and -transform elements

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>