riscv: Handle SBI calls forwarded to user space

The kernel KVM RISC-V module will forward certain SBI calls
to user space. These forwared SBI calls will usually be the
SBI calls which cannot be emulated in kernel space such as
PUTCHAR and GETCHAR calls.

This patch extends kvm_cpu__handle_exit() to handle SBI calls
forwarded to user space.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Link: https://lore.kernel.org/r/20211119124515.89439-8-anup.patel@wdc.com


Signed-off-by: Will Deacon <will@kernel.org>