kbuild: fixup genksyms usage/getopt

The usage does not mention the "-a,--arch" or "-T,--dump-types" options, so
add them.  The calls to getopt() seem to mention options that no longer exist
(some "k" and "p" thingy) but omits the "h" option which means using '-h'
actually triggers the error code path, so update those as well.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>