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>

board/emulation/qemu-riscv/Kconfig

@@ -7,7 +7,7 @@ config SYS_VENDOR
 	default "emulation"
 
 config SYS_CPU
-	default "qemu"
+	default "generic"
 
 config SYS_CONFIG_NAME
 	default "qemu-riscv"
@@ -18,7 +18,7 @@ config SYS_TEXT_BASE
 
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
-	select QEMU_RISCV
+	select GENERIC_RISCV
 	imply SYS_NS16550
 	imply VIRTIO_MMIO
 	imply VIRTIO_NET