riscv: start to use the configstring functions

These functions will allow us to remove hardcodes,
as long as we can verify the qemu and lowrisc targets
implement the configstring correctly. Hence, for the
most part, we'll start with mainboard changes first.

Define a new config variable, CONFIG_RISCV_CONFIGSTRING,
which has a default value that works on all existing
systems but which can be changed
as needed for a new SOC or mainboard.

Change-Id: I7dd3f553d3e61f1c49752fb04402b134fdfdf979
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/17256
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

src/commonlib/configstring.c

@@ -28,7 +28,6 @@
  */
 
 #include <config.h>
-#include <assert.h>
 #include <string.h>
 #include <commonlib/configstring.h>
 
@@ -49,6 +48,6 @@ void query_rtc(const char *config_string, uintptr_t *mtime)
 
 const char *configstring(void)
 {
-	uint32_t addr = *(uint32_t *)CONFIG_ARCH_CONFIGSTRING_RISCV;
+	uint32_t addr = *(uint32_t *)CONFIG_RISCV_CONFIGSTRING;
 	return (const char *)(uintptr_t)addr;
 }