pmdomain: renesas: use menu for Renesas

Current Renesas PM Domains appears on top page. Let's create new
menu for Renesas.

Signed-off-by: Kuninori Morimoto <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/pmdomain/renesas/Kconfig

···
 # SPDX-License-Identifier: GPL-2.0
 if SOC_RENESAS
+menu "Renesas PM Domains"
 
 config SYSC_RCAR
 	bool "System Controller support for R-Car" if COMPILE_TEST
···
 	bool "System Controller support for RZ/G2N" if COMPILE_TEST
 	select SYSC_RCAR
 
+endmenu
 endif