sim: frv: clean up redundant test coverage

sim: frv: clean up redundant test coverage

The frv-elf subdir contained five tests:
* cache: A cache test of some sort.
* exit47: A program to test exit status of 47 from sim.
* grloop: Some basic limited loop test program.
* hello: Standard "hello world" output program.
* loop: An infinite loop program.

The loop.s test is never referenced anywhere, and is all of 2 lines.
Anyone who really needs a while(1); test case and re-implement it
themselves locally.

The cache.s code isn't referenced anywhere because it requires some
custom args to the run program, and when this testcase was added, we
didn't have any support for that.  We do now, so we can add a header
to enable that.  Turns out the code crashes even with those, so turn
around and mark it xfail.  Maybe someone someday will care.

That leaves the small exit47, grloop, and hello tests.  Now that the
sim test harness supports testing for custom exit status, we can move
them all to sim/frv/ to maintain test coverage.

The remaining differences between frv-elf & sim/frv are:
* frv-elf/ runs for frv-*-elf while sim/frv/ runs for frv*-*-*.
* frv-elf/ runs "*.s" files while sim/frv/ only has .cgs and such.

On closer inspection, these are also meaningless distinctions:
* There is nothing specific to the tests that require an *-elf
  target.  Normally that would mean newlib+libgloss type stuff,
  but there's no such requirement in frv-elf/.
* The ".s" suffix is the standard "this is an assembly file" suffix.
  Since FRV is a CGEN target, we can reuse the existing convention of
  ".ms" to mean "miscellaneous .s" as in "this is an assembly file,
  and run/bucket its test results in the miscellaneous category".

So moving frv-elf/{cache,exit47,grloop,hello}.s to sim/frv/*.ms makes
sense and simplifies things quite a bit for the target while also
slightly increasing the coverage for some tuples.