riscv: sbi: Move sbi_probe_extension() out of CONFIG_SBI_V01

sbi_probe_extension() is an API defined in SBI v0.2, not v0.1.

Fixes 7e249bc1: ("riscv: Move all SMP related SBI calls to SBI_v01")
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Rick Chen <rick@andestech.com>