qemu-riscv: add preram_cbmem_console

Miraculously a console is being compiled in for romstage.
However, as no calls were potentially printing to the preram
console this was being ignored. Instead provide the symbol
required so as not to fail the build.

Change-Id: Id8f0b6e6d15b41fa7fe1b63bf2d91f15baa0edda
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/8712
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/riscv/romstage.ld

@@ -76,7 +76,7 @@ SECTIONS
 
 	_end = .;
 
-	/*preram_cbmem_console = CONFIG_CONSOLE_PRERAM_BUFFER_BASE;*/
+	preram_cbmem_console = CONFIG_CONSOLE_PRERAM_BUFFER_BASE;
 
 	/* Discard the sections we don't need/want */
 	/DISCARD/ : {