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/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a8a61a9..b3d7fd8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -20,6 +20,9 @@
 config TARGET_SIFIVE_UNLEASHED
 	bool "Support SiFive Unleashed Board"
 
+config TARGET_SIFIVE_UNMATCHED
+	bool "Support SiFive Unmatched Board"
+
 config TARGET_SIPEED_MAIX
 	bool "Support Sipeed Maix Board"
 
@@ -56,6 +59,7 @@
 source "board/emulation/qemu-riscv/Kconfig"
 source "board/microchip/mpfs_icicle/Kconfig"
 source "board/sifive/unleashed/Kconfig"
+source "board/sifive/unmatched/Kconfig"
 source "board/sipeed/maix/Kconfig"
 
 # platform-specific options below