riscv vmm: clean up SBI return code

[br]

Summary

Use C return in SBI handlers and clean up a bit

[br]

style: end of function return SUCCESS unless switch statement hit FAILURE

[jrtc27]

This doesn't seem to conform to the spec.

An ECALL with an unsupported SBI extension ID (EID) or an unsupported SBI function ID (FID) must return the error code SBI_ERR_NOT_SUPPORTED.

SBI_ERR_INVALID_PARAM Either hart_mask_base, or at least one hartid from hart_mask, is not valid, i.e. either the hartid is not enabled by the platform or is not available to the supervisor.

(this one's a "may return", but I think best to do so)

(but note hart_mask_base of -1 means all harts, and hart_mask is ignored)

sys/riscv/vmm/vmm_sbi.c

160–161

Not for *this* change, but can you please implement this properly? It should not have landed with this TODO...

[br]

Address @jrtc27 comments

• riscv_send_ipi() now takes cpuset* as an argument
• SBI error codes fixed with respect to the spec