It depends on the board implementation whether to have each pins of
CTS/RTS, and others for modem. So it is necessary to divide current
uart_ctsrts group into uart_ctsrts and uart_modem groups.

Since the number of implemented pins for modem differs depending
on SoC, each uart_modem group also has a different number of pins.
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/1564465410-9165-2-git-send-email-hayashi.kunihiko@socionext.comAcked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>