Define better error codes for TEE SBI calls

[abrestic-rivos]

We've been mostly using the existing SBI error codes as defined in v1.0 of the spec, but the TEE API is much larger and more complex than any existing extension, and there are several cases where we're over-using e.g. INVALID_PARAM or INVALID_ADDRESS where we could be providing a more useful error code that would be more helpful while debugging.

Some possible examples of where we could do a better job:

• OUT_OF_PAGES when the map_*_pages() calls fail due to being out page-table pages.
• ALREADY_MAPPED or ALREADY_CONVERTED in the cases where a map or conversion operation (partially) specifies memory that was already mapped/converted.
• error codes (e.g. NOT_RUNNABLE) to communicate that a vCPU or VM is not in the proper lifecycle state.
• BUSY or IN_PROGRESS for operations that fail because it's already going on elsewhere, for example running a vCPU or initiating a fence.
• UNSUPPORTED_PAGE_SIZE for operations that take page sizes and the requested page size isn't supported by the TSM

This has been coming up a bunch in the review of the spec doc at riscv-non-isa/riscv-ap-tee#5.

cc @rsahita @atulkharerivos @atishp04

[atulkharerivos]

SGTM; will take this up and the associated code changes.