The genksyms command part in cmd_gensymtypes_{c,S} is duplicated.
Factor it out into the 'genksyms' macro.

For the readability, I slightly refactor the arguments to genksyms.
Signed-off-by: NMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: NNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: NNicolas Schier <nicolas@fjasle.eu>