doc: mkimage: Rearrange/remove some options

This moves some options which work in any mode to the general options
section. -p is moved to after -E/-B since those options are related. This
also adds documentation for -h and -V.

The -F, -l, and -G options are documented twice. Remove the second
documentation in each case. The synopsis for -l also suggests an implied
second uimage-file-name parameter. E.g.

	mkimage [-l uimage-file-name] uimage-file-name

This is misleading, so remove it. Wrap a few lines to 80 characters as
well.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>