riscv: Rename cpu/qemu to cpu/generic

The QEMU CPU support under arch/riscv is pretty much generic
and works fine for SiFive Unleashed as well. In fact, there
will be quite a few RISC-V SOCs for which QEMU CPU support
will work fine.

This patch renames cpu/qemu to cpu/generic to indicate the
above fact. If there are SOC specific errata workarounds
required in cpu/generic then those can be done at runtime
in cpu/generic based on CPU vendor specific DT compatible
string.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c45e4d7..6879047 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -22,7 +22,7 @@
 
 # platform-specific options below
 source "arch/riscv/cpu/ax25/Kconfig"
-source "arch/riscv/cpu/qemu/Kconfig"
+source "arch/riscv/cpu/generic/Kconfig"
 
 # architecture-specific options below