riscv: don't allow selecting SBI based drivers for M-mode

When running in M-mode we can't use SBI based drivers.  Add a new
CONFIG_RISCV_SBI that drivers that do SBI calls can depend on
instead.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/Kconfig

@@ -76,6 +76,12 @@ config ARCH_MMAP_RND_BITS_MAX
 config RISCV_M_MODE
 	bool
 
+# set if we are running in S-mode and can use SBI calls
+config RISCV_SBI
+	bool
+	depends on !RISCV_M_MODE
+	default y
+
 config MMU
 	def_bool y
 

drivers/tty/hvc/Kconfig

@@ -89,7 +89,7 @@ config HVC_DCC
 
 config HVC_RISCV_SBI
 	bool "RISC-V SBI console support"
-	depends on RISCV
+	depends on RISCV_SBI
 	select HVC_DRIVER
 	help
 	  This enables support for console output via RISC-V SBI calls, which

drivers/tty/serial/Kconfig

@@ -88,7 +88,7 @@ config SERIAL_EARLYCON_ARM_SEMIHOST
 
 config SERIAL_EARLYCON_RISCV_SBI
 	bool "Early console using RISC-V SBI"
-	depends on RISCV
+	depends on RISCV_SBI
 	select SERIAL_CORE
 	select SERIAL_CORE_CONSOLE
 	select SERIAL_EARLYCON