arch/riscv: Make RISCV specific options depend on ARCH_RISCV

Also don't define the default as this results in spurious lines in the
.config.

The only difference in the generated config.h is that for most board
ARCH_RISCV_M goes from 1 to 0. This should not matter.

Change-Id: I3e8c1cc5696d621e243696a3b5e34f62ab69a688
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31311
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/riscv/Kconfig

@@ -1,6 +1,15 @@
+config ARCH_RISCV_RV64
+	bool
+	select ARCH_RISCV
+
+config ARCH_RISCV_RV32
+	bool
+	select ARCH_RISCV
+
 config ARCH_RISCV
 	bool
-	default n
+
+if ARCH_RISCV
 
 config RISCV_ARCH
 	string
@@ -37,16 +46,6 @@ config ARCH_RISCV_U
 	bool
 	default n
 
-config ARCH_RISCV_RV64
-	bool
-	default n
-	select ARCH_RISCV
-
-config ARCH_RISCV_RV32
-	bool
-	default n
-	select ARCH_RISCV
-
 config ARCH_RISCV_PMP
 	bool
 	default n
@@ -74,3 +73,5 @@ config RISCV_USE_ARCH_TIMER
 
 config RISCV_WORKING_HARTID
 	int
+
+endif # if ARCH_RISCV