riscv: qemu: Add platform-specific Kconfig options

Add the QEMU RISC-V platform-specific Kconfig options, to include
CPU and timer drivers.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7dc6e3f..39ca2d8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -22,6 +22,7 @@
 
 # platform-specific options below
 source "arch/riscv/cpu/ax25/Kconfig"
+source "arch/riscv/cpu/qemu/Kconfig"
 
 # architecture-specific options below