azure/gitlab/travis: Add RISC-V SPL testing

This adds QEMU RISC-V 32/64 SPL testing. Unlike QEMU RISC-V 32/64,
we test SPL running in M-mode and U-Boot proper running in S-mode,
with a 4-core SMP configuration.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>