CBMEM console: Fix and enhance pre-RAM support

Use the value of CONSOLE_PRERAM_BUFFER_SIZE to determine if we can
do CBMEM console in bootblock and romstage. Kconfig forces it to zero
if _BASE is unset or we cannot do CAR migration on x86.

Add CBMEM console to bootblock, except for x86. Only one of bootblock
and romstage clears the pre-RAM buffer.

To start with empty console log on S3 wakeup, ramstage now clears
previous contents of CBMEM buffer if there was no pre-RAM buffer.

Unify Kconfig variable naming.

TODO: ARM configurations do not define PRERAM_BUFFER_BASE values.

Change-Id: I70d82da629529dbfd7bc9491223abd703cbc0115
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7862
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/include/console/cbmem_console.h

@@ -32,7 +32,8 @@ static inline void cbmemc_reinit(void) {}
 #endif
 
 #define __CBMEM_CONSOLE_ENABLE__	CONFIG_CONSOLE_CBMEM && \
-	((ENV_ROMSTAGE && !CONFIG_BROKEN_CAR_MIGRATE) || ENV_RAMSTAGE)
+	(ENV_RAMSTAGE || (CONFIG_CONSOLE_PRERAM_BUFFER_SIZE && \
+	((ENV_BOOTBLOCK && CONFIG_BOOTBLOCK_CONSOLE) || ENV_ROMSTAGE)))
 
 #if __CBMEM_CONSOLE_ENABLE__
 static inline void __cbmemc_init(void)	{ cbmemc_init(); }