riscv, qemu_fw_cfg: Add support for RISC-V architecture

Qemu fw_cfg support was missing for RISC-V, which made it hard to do
proper vmcore dumps from qemu.

Add the missing RISC-V arch-defines.

You can now do vmcore dumps from qemu. Add "-device vmcoreinfo" to the
qemu command-line. From the qemu monitor:
  (qemu) dump-guest-memory vmcore

The vmcore can now be used, e.g., with the "crash" utility.
Acked-by: "Michael S. Tsirkin" <mst@redhat.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Clément Léger <cleger@rivosinc.com>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Message-Id: <20231012102852.234442-1-bjorn@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/firmware/Kconfig

@@ -155,7 +155,7 @@ config RASPBERRYPI_FIRMWARE
 
 config FW_CFG_SYSFS
 	tristate "QEMU fw_cfg device support in sysfs"
-	depends on SYSFS && (ARM || ARM64 || PARISC || PPC_PMAC || SPARC || X86)
+	depends on SYSFS && (ARM || ARM64 || PARISC || PPC_PMAC || RISCV || SPARC || X86)
 	depends on HAS_IOPORT_MAP
 	default n
 	help

drivers/firmware/qemu_fw_cfg.c

@@ -211,7 +211,7 @@ static void fw_cfg_io_cleanup(void)
 
 /* arch-specific ctrl & data register offsets are not available in ACPI, DT */
 #if !(defined(FW_CFG_CTRL_OFF) && defined(FW_CFG_DATA_OFF))
-# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64))
+# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64) || defined(CONFIG_RISCV))
 #  define FW_CFG_CTRL_OFF 0x08
 #  define FW_CFG_DATA_OFF 0x00
 #  define FW_CFG_DMA_OFF 0x10