Adding Vector Context xtest - #827

Add TA_OS_TEST_CMD_RISCV_VEC_CONTEXT and the sub-tests behind it.

A TA runs with the vector unit disabled and is given it on the first
vector instruction, or vector CSR access, it executes, so every sub-test
starts by taking that trap. What they then cover is:

  SYSCALL      the whole register file and the vector CSRs across
               TEE_SCN_WAIT, issued through a bare ecall so that nothing
               the compiler generated runs in between; the syscall
               suspends the thread, runs the normal world, and resumes
               through thread_resume_from_rpc()
  CSR_FIRST    reads vlenb before issuing any vector instruction, which
               traps with VS Off exactly as an instruction would, so a
               TEE that decodes only the instructions kills the TA here
               instead of handing it a context; then checks the register
               file it was given is clear
  TAINT        leaves a pattern in the registers and returns
  CHECK_TAINT  reads the registers before writing any of them and fails
               if an earlier TA's pattern is still there

On failure the index of the first register that did not survive is
reported back to the caller, along with vlenb, so a failure says which
register was lost and how wide it was.

Everything returns TEE_ERROR_NOT_SUPPORTED on a target without the
vector extension.

Signed-off-by: Dave Patel <dave.patel@riscstar.com>
(cherry picked from commit 609de38a294ee088eadfa02db822d46d082a29ac)

Drive the os_test sub-tests from xtest and add the checks that can only
be made from the normal world.

Alongside the TA side cases the test holds a pattern in this process'
vector registers across a call into the TEE, run twice: once against a TA
command that uses vector and once against one that does not, since the
TEE puts the normal world context back in the first case and skips the
restore in the second, having never disturbed the registers.

That half needs xtest itself to be built for a hart with the vector
extension, which is a property of the toolchain the normal world was
built with rather than of what the TEE supports. Where it is missing the
two sub-cases are compiled out and the test says so rather than passing
quietly.

A concurrency case runs the syscall sub-test from several threads at
once, since the vector bookkeeping is per OP-TEE thread and one thread's
context must not surface in another.

Signed-off-by: Dave Patel <dave.patel@riscstar.com>
(cherry picked from commit 6a0cc5985a38013734db42d6d5d4ca21a580fd31)