uboot-phytec

riscv: Introduce a Kconfig option for machine mode

So far we have a Kconfig option for supervisor mode. This adds an
option for the machine mode.

Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>