riscv: Introduce a Kconfig option for machine mode

So far we have a Kconfig option for supervisor mode. This adds an
option for the machine mode.
Signed-off-by: NAnup Patel <anup@brainfault.org>
Signed-off-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NLukas Auer <lukas.auer@aisec.fraunhofer.de>

arch/riscv/Kconfig

@@ -62,6 +62,22 @@ config CMODEL_MEDANY
 
 endchoice
 
+choice
+	prompt "Run Mode"
+	default RISCV_MMODE
+
+config RISCV_MMODE
+	bool "Machine"
+	help
+	  Choose this option to build U-Boot for RISC-V M-Mode.
+
+config RISCV_SMODE
+	bool "Supervisor"
+	help
+	  Choose this option to build U-Boot for RISC-V S-Mode.
+
+endchoice
+
 config RISCV_ISA_C
 	bool "Emit compressed instructions"
 	default y
@@ -73,11 +89,6 @@ config RISCV_ISA_C
 config RISCV_ISA_A
 	def_bool y
 
-config RISCV_SMODE
-	bool "Run in S-Mode"
-	help
-	  Enable this option to build U-Boot for RISC-V S-Mode
-
 config 32BIT
 	bool