tty: hvc: Don't enable the RISC-V SBI console by default

The new SBI console has the same problem as the old one: there's only
one shared backing hardware and no synchronization, so the two drivers
end up stepping on each other.  This was the same issue the old SBI-0.1
console drivers had, but that was disabled by default when SBI-0.1 was.

So just mark the new driver as nonportable.
Reported-by: Emil Renner Berthing <kernel@esmil.dk>
Fixes: 88ead68e ("tty: Add SBI debug console support to HVC SBI driver")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240214153429.16484-2-palmer@rivosinc.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/hvc/Kconfig

@@ -108,13 +108,15 @@ config HVC_DCC_SERIALIZE_SMP
 
 config HVC_RISCV_SBI
 	bool "RISC-V SBI console support"
-	depends on RISCV_SBI
+	depends on RISCV_SBI && NONPORTABLE
 	select HVC_DRIVER
 	help
 	  This enables support for console output via RISC-V SBI calls, which
-	  is normally used only during boot to output printk.
+	  is normally used only during boot to output printk.  This driver
+	  conflicts with real console drivers and should not be enabled on
+	  systems that directly access the console.
 
-	  If you don't know what do to here, say Y.
+	  If you don't know what do to here, say N.
 
 config HVCS
 	tristate "IBM Hypervisor Virtual Console Server support"