riscv: Enable SPI flash env for SiFive Unmatched.

Enable saving environment to SPI flash memory on SiFive
Unmatched.

Signed-off-by: Thomas Skibo <thomas-git@skibo.net>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/cpu/fu740/Kconfig b/arch/riscv/cpu/fu740/Kconfig
index 049a0a0..3e0c1fd 100644
--- a/arch/riscv/cpu/fu740/Kconfig
+++ b/arch/riscv/cpu/fu740/Kconfig
@@ -40,3 +40,16 @@
 	imply DM_I2C
 	imply SYS_I2C_OCORES
 	imply SPL_I2C
+
+if ENV_IS_IN_SPI_FLASH
+
+config ENV_OFFSET
+	default 0x505000
+
+config ENV_SIZE
+	default 0x20000
+
+config ENV_SECT_SIZE
+	default 0x10000
+
+endif # ENV_IS_IN_SPI_FLASH