riscv: qemu: add SPL configuration

Add two new configurations (qemu-riscv{32,64}_spl_defconfig) with SPL
enabled for RISC-V QEMU. QEMU does not require SPL to run U-Boot. The
configurations are meant to help the development of SPL on RISC-V.

The configurations enable RAM as the only SPL boot device. Images must
be loaded at address 0x80200000. In the default boot flow, U-Boot SPL
starts in machine mode, loads the OpenSBI FW_DYNAMIC firmware and U-Boot
proper from the supplied FIT image, and starts OpenSBI. U-Boot proper is
then started in supervisor mode by OpenSBI.

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
diff --git a/board/emulation/qemu-riscv/MAINTAINERS b/board/emulation/qemu-riscv/MAINTAINERS
index c701c83..78969ed 100644
--- a/board/emulation/qemu-riscv/MAINTAINERS
+++ b/board/emulation/qemu-riscv/MAINTAINERS
@@ -5,5 +5,7 @@
 F:	include/configs/qemu-riscv.h
 F:	configs/qemu-riscv32_defconfig
 F:	configs/qemu-riscv32_smode_defconfig
+F:	configs/qemu-riscv32_spl_defconfig
 F:	configs/qemu-riscv64_defconfig
 F:	configs/qemu-riscv64_smode_defconfig
+F:	configs/qemu-riscv64_spl_defconfig