easylogo: clean up some more and add -r (rgb) support

Michael Hennerich added support for outputting an image in RGB format rather
than forcing YUYV all the time.  This makes obvious sense if the display you
have takes RGB input rather than YUYV.

Rather than hack in support for options, I've converted it to use getopt and
cleaned up the argument parsing in the process.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>