riscv: Rework riscv_cpu_probe for current event macros

This function should now be a EVENT_SPY_SIMPLE call, update it.

Tested-by: Milan P. Stanić <mps@arvanta.net>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Signed-off-by: Tom Rini <trini@konsulko.com>