uboot-imx

cpu: Add a RISC-V CPU driver

This adds a driver for RISC-V CPU. Note the driver will bind
a RISC-V timer driver if "timebase-frequency" property is
present in the device tree.

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