configs: reset: fu540: enable dm reset framework for SiFive

Add necessary defconfig and Kconfig entries to enable SiFive SoC's
reset driver so as to utilise U-Boot's reset framework.

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Reviewed-by: Pragnesh Patel <Pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Bin Meng <bin.meng@windriver.com>