riscv: qemu: enable CONFIG_CMD_BOOTEFI_SELFTEST

Enable CONFIG_CMD_BOOTEFI_SELFTEST for the QEMU RISC-V boards.

Travis CI QEMU testing has been enabled for qemu-riscv64_defconfig. With
this patch we will test the UEFI sub-system on the board.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>