Azure/GitLab: Move to gcc-11.1.0 and LLVM-11

- Move to gcc-11.1.0 builds from kernel.org for supported platforms and
  LLVM-11 for those tests.
- grub-2.06 does not build with gcc-11.1.0 on riscv32 as seen here:
  https://www.mail-archive.com/grub-devel@gnu.org/msg30736.html


  so drop it.
- Update to newer Xtensa (gcc-9.2.0) and ARC (gcc-10.2) toolchains

Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
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Changes in v2:
- Switch to gcc-11.1.0 builds rather than pre-release
- grub-2.06 is out, use that rather than -rc1
- Update Xtensa and ARC toolchains.