The SBI v0.2 contains some of the improved versions of required v0.1
extensions such as remote fence, timer and IPI.

This patch implements those extensions.
Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>