riscv: sifive: fu740: Support i2c in spl

Enable SPL_I2C_SUPPORT for fu740, and add 'u-boot,dm-spl' property in
i2c node.

Signed-off-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/cpu/fu740/Kconfig b/arch/riscv/cpu/fu740/Kconfig
index 1dc052b..8e54310 100644
--- a/arch/riscv/cpu/fu740/Kconfig
+++ b/arch/riscv/cpu/fu740/Kconfig
@@ -37,3 +37,4 @@
 	imply PWM_SIFIVE
 	imply DM_I2C
 	imply SYS_I2C_OCORES
+	imply SPL_I2C_SUPPORT