board: sifive: add HiFive Unmatched board support

Add defconfig and board support for HiFive Unmatched.

Signed-off-by: Green Wan <green.wan@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index 91303ec..a42b3f0 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -166,7 +166,7 @@
 
 config RESET_SIFIVE
 	bool "Reset Driver for SiFive SoC's"
-	depends on DM_RESET && CLK_SIFIVE_PRCI && TARGET_SIFIVE_UNLEASHED
+	depends on DM_RESET && CLK_SIFIVE_PRCI && (TARGET_SIFIVE_UNLEASHED || TARGET_SIFIVE_UNMATCHED)
 	default y
 	help
 	  PRCI module within SiFive SoC's provides mechanism to reset