ARM: shmobile: defconfig: Supplement DTB with ATAG information

ARM: shmobile: defconfig: Supplement DTB with ATAG information

Enable CONFIG_ARM_ATAG_DTB_COMPAT to allow U-Boot to override kernel
command line from DTB using the bootargs argument.  This is needed at
least on R-Car H1 Marzen to control the command line from U-Boot.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250116153204.615736-1-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>